opinion: Lori SCIALABBA, Acting Director, United States Citizenship and Immigration Services, et al., Petitioners
  v.
  Rosalina CUELLAR DE OSORIO et al.
  No. 12-930.
  Supreme Court of the United States
  Argued Dec. 10, 2013.
  Decided June 9, 2014.
  Syllabus*
  The Immigration and Nationality Act permits qualifying U.S. citizens and lawful permanent residents (LPRs) to petition for certain family members to obtain immigrant visas. A sponsored individual, known as the principal beneficiary, is placed into a "family preference" category based on his relationship with the petitioner. 8 U.S.C. §§ 1153(a)(1)-(4). The principal beneficiary's spouse and minor children in turn qualify as derivative beneficiaries, "entitled to the same status" and "order of consideration" as the principal. § 1153(d). The beneficiaries then become eligible to apply for visas in order of "priority date"-that is, the date a petition was filed. § 1153(e)(1). Because the immigration process often takes years or decades to complete, a child seeking to immigrate may "age out"- i.e., reach adulthood and lose her immigration status-before she reaches the front of the visa queue. The Child Status Protection Act (CSPA) sets forth a remedy in that circumstance, providing that "[i]f the age of an alien is determined ... to be 21 years of age or older," notwithstanding certain allowances for bureaucratic delay, §§ 1153(h)(1)-(2), "the alien's petition shall automatically be converted to the appropriate category and the alien shall retain the original priority date issued upon receipt of the original petition." § 1153(h)(3).
  Respondents, principal beneficiaries who became LPRs, filed petitions for their aged-out children, asserting that the newly filed petitions should receive the same priority date as their original petitions. Instead, U.S. Citizenship and Immigration Services (USCIS) gave the new petitions current priority dates. The District Court granted the Government summary judgment, deferring to the Board of Immigration Appeals' (BIA's) determination that only those petitions that can be seamlessly converted from one family preference category to another without the need for a new sponsor are entitled to conversion under § 1153(h)(3). The en banc Ninth Circuit reversed, holding that the provision unambiguously entitled all aged-out derivative beneficiaries to automatic conversion and priority date retention.
  Held : The judgment is reversed, and the case is remanded.
  695 F.3d 1003, reversed and remanded.
  Justice KAGAN, joined by Justice KENNEDY and Justice GINSBURG, concluded that the BIA's textually reasonable construction of § 1153(h)(3)'s ambiguous language was entitled to deference. Pp. 2203 - 2213.
  (a) Because § 1153(h)(3) does not speak unambiguously to the issue here, a court must defer to the BIA's reasonable interpretation. See Chevron U.S.A. Inc. v. Natural Resources Defense Council, Inc., 467 U.S. 837, 844, 104 S.Ct. 2778, 81 L.Ed.2d 694. The first clause of § 1153(h)(3) states a condition that encompasses every aged-out beneficiary of a family preference petition. The second clause, however, does not easily cohere with the first. It prescribes a remedy that can apply to only a subset of the beneficiaries described in the first clause. This remedial prescription directs immigration officials to take the alien's petition and convert it from a category benefitting a child to an appropriate category for adults, without any change in the petition, including its sponsor, or any new filing. Moreover, this conversion is to be "automati[c]"-that is, one involving no additional decisions, contingencies, or delays. Thus, the only aliens who may benefit from § 1153(h)(3)'s back half are those for whom automatic conversion is possible.
  The understanding that "automatic conversion" entails nothing more than picking up the petition from one category and dropping it into another for which the alien now qualifies matches the exclusive way immigration law used the term when § 1153(h)(3) was enacted. See 8 CFR § 204.2(i)(1)-(3) (2002). And Congress used the word "conversion" in the identical way elsewhere in the CSPA. See, e.g., §§ 1151(f)(2), (3).
  If the term meant more than that in § 1153(h)(3), it would undermine the family preference system's core premise: that each immigrant must have a qualified and willing sponsor. See §§ 1154(a), (b). If an original sponsor does not have a legally recognized relationship with the aged-out derivative beneficiary, another sponsor, e.g., the old principal beneficiary, must be swapped in for the alien to qualify for a new family preference category. But immigration officials cannot assume that a new sponsor is eligible and willing to petition on the alien's behalf, given the numerous requirements the law imposes on family preference petitioners. See, e.g., § 1154(a)(1)(B)(i)(II). Neither can they figure out whether a valid sponsor exists unless he files and USCIS approves a new petition-the very thing § 1153(h)(3) says is not required.
  In any case, a new qualified sponsor will rarely exist at the requisite time. An alien is deemed to age out on "the date on which an immigrant visa number became available for the alien's parent." § 1153(h)(1)(A). Since aging out triggers automatic conversion, the date of automatic conversion is best viewed as the same. But at that time, the aged-out beneficiary's parent cannot yet be a citizen or LPR, and so no new, qualified sponsor will be ready to step into the old one's shoes.
  On the above account, § 1153(h)(3)'s second clause provides a remedy to those principal and derivative beneficiaries who had a qualifying relationship with an LPR both before and after they aged out. In contrast, aliens like respondents' children-the nieces, nephews, and grandchildren of the initial sponsors-cannot qualify for "automatic conversion": they lacked a qualifying preference relationship with the initial petitioner, and so cannot fit into a new preference category without obtaining a new sponsor.
  The ambiguity created by § 1153(h)(3)'s ill-fitting clauses left the BIA to choose how to reconcile the statute's different commands. It reasonably opted to abide by the inherent limits of § 1153(h)(3)'s remedial clause, rather than go beyond those limits so as to match the sweep of the first clause's condition. When an agency thus resolves statutory tension, ordinary principles of administrative deference require this Court to defer. See National Assn. of Home Builders v. Defenders of Wildlife, 551 U.S. 644, 666, 127 S.Ct. 2518, 168 L.Ed.2d 467. Pp. 2203 - 2207
  (b) Respondents take issue with the BIA's interpretation, but none of their contentions is persuasive. Pp. 2207 - 2213.
  (1) Respondents aver that every aged-out beneficiary could be automatically converted if immigration officials substituted new sponsors and managed the timing of conversion so that a new sponsor existed on the relevant date. These administrative maneuvers are not in keeping with the natural and long-established meaning of "automatic conversion," they require conversion to occur on a date that has no connection to the alien's aging out, and they demand administrative juggling to make automatic conversion work. And that painstakingly managed process still cannot succeed because a derivative's parent may never become able to sponsor a visa-and immigration officials cannot practicably tell whether a given parent has done so. Pp. 2207 - 2210.
  (2) Respondents argue that the word "and" in the second clause of § 1153(h)(3) indicates that priority date retention is a benefit wholly independent of automatic conversion. But "and" does not necessarily disjoin two phrases, and context suggests that the instructions work in tandem. In other statutory and regulatory provisions respecting "conversions," retention of a priority date is conditional on a conversion occurring. See, e.g., §§ 1154(k)(1)-(3). Respondent's reading would make priority date retention conditional on something the statute nowhere mentions. And it would engender unusual results that, without some clearer statement, the Court cannot conclude that Congress intended. Pp. 2210 - 2212.
  (3) Finally, respondents contend that, assuming § 1153(h)(3) is ambiguous, the BIA acted unreasonably in choosing the more restrictive reading. But the BIA's interpretation benefits from administrative simplicity and fits with immigration law's basic first-come, first-served rule. By contrast, respondents would scramble the priority order Congress established by allowing aged-out derivative beneficiaries, like respondents' sons and daughters, to enter the visa queue ahead of beneficiaries who had a qualifying relationship with an LPR for a far longer time. Pp. 2212 - 2213.
  THE CHIEF JUSTICE, joined by Justice SCALIA, agreed that the BIA's interpretation was reasonable, but not because an agency has authority to resolve direct conflicts within a statute. There is no conflict or internal tension in § 1153(h)(3). The first clause of the provision defines the persons potentially affected, but does not grant anything to anyone. The particular benefit provided by the statute-automatic conversion and retention of priority date-is found exclusively in the second clause, and that relief requires, at minimum, that an aged-out beneficiary have his own eligible sponsor who is committed to providing financial support for the beneficiary. Beyond that, Congress did not speak clearly to which petitions can be automatically converted. The BIA's reasonable interpretation of § 1153(h)(3) is consistent with the ordinary meaning of the statutory terms, with the established meaning of automatic conversion in immigration law, and with the structure of the family-based immigration system. Pp. 2214 - 2216.
  KAGAN, J., announced the judgment of the Court and delivered an opinion, in which KENNEDY and GINSBURG, JJ., joined. ROBERTS, C.J., filed an opinion concurring in the judgment, in which SCALIA, J., joined. ALITO, J., filed a dissenting opinion. SOTOMAYOR, J., filed a dissenting opinion, in which BREYER, J., joined, and in which THOMAS, J., joined except as to footnote 3.
  
  Elaine J. Goldenberg, for Petitioners.
  Mark C. Fleming, Boston, MA, for Respondents.
  
  Donald B. Verrilli, Jr., Solicitor General, Counsel of Record, Department of Justice, Washington, D.C., for Petitioners.
  Paul R.Q. Wolfson, Megan Barbero, Christina Manfredi McKinley, Ari Holtzblatt, Wilmer Cutler Pickering Hale and Dorr LLP, Washington, D.C., Jason D. Hirsch, Wilmer Cutler Pickering, Hale and Dorr LLP, New York, NY, Mark C. Fleming, Counsel of Record, Harriet A. Hoder, Wilmer Cutler Pickering Hale and Dorr LLP, Boston, MA, Carl Shusterman, Amy Prokop, Law Offices of Carl Shusterman, Los Angeles, CA, Nancy E. Miller, Robert L. Reeves, Eric R. Welsh, Reeves & Associates, Pasadena, CA, for Respondents.
  Donald B. Verrilli, Jr., Solicitor General, Counsel of Record, Stuart F. Delery, Assistant Attorney General, Edwin S. Kneedler, Deputy Solicitor General, Elaine J. Goldenberg, Assistant to the Solicitor General, Elizabeth J. Stevens, Gisela A. Westwater, Attorneys, Department of Justice, Washington, D.C., for Petitioners.
  Justice KAGAN announced the judgment of the Court and delivered an opinion, in which Justice KENNEDY and Justice GINSBURG join.
  Under the Immigration and Nationality Act, 8 U.S.C. § 1101 et seq., citizens and lawful permanent residents (LPRs) of the United States may petition for certain family members-spouses, siblings, and children of various ages-to obtain immigrant visas. Such a sponsored individual is known as the petition's principal beneficiary. In turn, any principal beneficiary's minor child-meaning an unmarried child under the age of 21-qualifies as a derivative beneficiary, "entitled to the same [immigration] status" and "order of consideration" as his parent. § 1153(d). Accordingly, when a visa becomes available to the petition's principal beneficiary, one also becomes available to her minor child.
  But what happens if, sometime after the relevant petition was filed, a minor child (whether a principal or a derivative beneficiary) has turned 21-or, in immigration lingo, has "aged out"? The immigration process may take years or even decades to complete, due in part to bureaucratic delays associated with reviewing immigration documents and in (still greater) part to long queues for the limited number of visas available each year. So someone who was a youngster at the start of the process may be an adult at the end, and no longer qualify for an immigration status given to minors. The Child Status Protection Act (CSPA), 116 Stat. 927, ensures that the time Government officials have spent processing immigration papers will not count against the beneficiary in assessing his status. See 8 U.S.C. § 1153(h)(1). But even with that provision, the beneficiary may age out solely because of the time he spent waiting in line for a visa to become available.
  The question presented in this case is whether the CSPA grants a remedy to all aliens who have thus outpaced the immigration process-that is, all aliens who counted as child beneficiaries when a sponsoring petition was filed, but no longer do so (even after excluding administrative delays) by the time they reach the front of the visa queue. The Board of Immigration Appeals (BIA or Board) said no. It interpreted the CSPA as providing relief to only a subset of that group-specifically, those aged-out aliens who qualified or could have qualified as principal beneficiaries of a visa petition, rather than only as derivative beneficiaries piggy-backing on a parent. We now uphold the Board's determination as a permissible construction of the statute.
  I
  A
  An alien needs an immigrant visa to enter and permanently reside in the United States. See § 1181(a).1 To obtain that highly sought-after document, the alien must fall within one of a limited number of immigration categories. See §§ 1151(a)-(b). The most favored is for the "immediate relatives" of U.S. citizens-their parents, spouses, and unmarried children under the age of 21. See §§ 1151(b)(2)(A)(i), 1101(b)(1). Five other categories-crucial to this case, and often denominated "preference" categories-are for "family-sponsored immigrants," who include more distant or independent relatives of U.S. citizens, and certain close relatives of LPRs. 2 Specifically, those family preference categories are:
  F1: the unmarried, adult (21 or over) sons and daughters of U.S. citizens;
  F2A: the spouses and unmarried, minor (under 21) children of LPRs;
  F2B: the unmarried, adult (21 or over) sons and daughters of LPRs;
  F3: the married sons and daughters of U.S. citizens;
  F4: the brothers and sisters of U.S. citizens. §§ 1151(a)(1), 1153(a)(1)-(4).3
  (A word to the wise: Dog-ear this page for easy reference, because these categories crop up regularly throughout this opinion.)
  The road to obtaining any family-based immigrant visa begins when a sponsoring U.S. citizen or LPR files a petition on behalf of a foreign relative, termed the principal beneficiary. See §§ 1154(a)(1)(A)(i), (a)(1)(B)(i)(I), (b); 8 CFR § 204.1(a)(1) (2014). The sponsor (otherwise known as the petitioner-we use the words interchangeably) must provide U.S. Citizenship and Immigration Services (USCIS) with evidence showing, among other things, that she has the necessary familial relationship with the beneficiary, see §§ 204.2(a)(2), (d)(2), (g)(2), and that she has not committed any conduct disqualifying her from sponsoring an alien for a visa, see, e.g.,8 U.S.C. § 1154(a)(1)(B)(i)(II) (barring an LPR from submitting a petition if she has committed certain offenses against minors). USCIS thereafter reviews the petition, and approves it if found to meet all requirements. See § 1154(b).
  For a family preference beneficiary, that approval results not in getting a visa then and there, but only in getting a place in line. (The case is different for "immediate relatives" of U.S. citizens, who can apply for and receive a visa as soon as a sponsoring petition is approved.) The law caps the number of visas issued each year in the five family preference categories, see §§ 1151(c)(1), 1152, 1153(a)(1)-(4), and demand regularly exceeds the supply. As a consequence, the principal beneficiary of an approved petition is placed in a queue with others in her category (F1, F2A, or what have you) in order of "priority date"-that is, the date a petition was filed with USCIS. See § 1153(e)(1); 8 CFR § 204.1(b); 22 CFR 42.53(a) (2013). Every month, the Department of State sets a cut-off date for each family preference category, indicating that visas (sometimes referred to by "visa numbers") are available for beneficiaries with priority dates earlier than the cut-off. See 8 CFR § 245.1(g)(1); 22 CFR § 42.51(b). The system is thus first-come, first-served within each preference category, with visas becoming available in order of priority date.
  Such a date may benefit not only the principal beneficiary of a family preference petition, but also her spouse and minor children. Those persons, labeled the petition's "derivative beneficiar[ies]," are "entitled to the same status, and the same order of consideration" as the principal. 8 U.S.C. §§ 1153(d), (h). Accordingly, when a visa becomes available for the principal, one becomes available for her spouse and minor children too. And that is so even when (as is usually but not always the case) the spouse and children would not qualify for any family preference category on their own. For example, the child of an F4 petition's principal beneficiary is the niece or nephew of a U.S. citizen, and federal immigration law does not recognize that relationship. Nonetheless, the child can piggy-back on his qualifying parent in seeking an immigrant visa-although, as will be further discussed, he may not immigrate without her. See 22 CFR § 40.1(a)(2); infra, at 2198, 2206 - 2207, 2212 - 2213.
  Once visas become available, the principal and any derivative beneficiaries must separately file visa applications. See 8 U.S.C. § 1202(a). Such an application requires an alien to demonstrate in various ways her admissibility to the United States. See, e.g., § 1182(a)(1)(A) (alien may not have serious health problems); § 1182(a)(2)(A) (alien may not have been convicted of certain crimes); § 1182(a)(3)(B) (alien may not have engaged in terrorist activity). Notably, one necessary showing involves the U.S. citizen or LPR who filed the initial petition: To mitigate any possibility of becoming a "public charge," the visa applicant (whether a principal or derivative beneficiary) must append an "affidavit of support" executed by that sponsoring individual. §§ 1182(a)(4)(C)(ii), 1183a(a)(1). Such an affidavit legally commits the sponsor to support the alien, usually for at least 10 years, with an annual income "not less than 125% of the federal poverty line." § 1183a(a)(1)(A); see §§ 1183a(a)(2)-(3).
  After the beneficiaries have filed their applications, a consular official reviews the documents and, if everything is in order, schedules in-person interviews. See § 1202(h). The interviews for a principal and her children (or spouse) usually occur back-to-back, although those for the children may also come later.4 The consular official will determine first whether the principal should receive a visa; if (but only if) the answer is yes, the official will then consider the derivatives' applications. See 22 CFR §§ 40.1(a)(2), 42.62, 42.81(a). Provided all goes well, everyone exits the consulate with visas in hand-but that still does not make them LPRs. See 8 U.S.C. § 1154(e). Each approved alien must then travel to the United States within a set time, undergo inspection, and confirm her admissibility. See §§ 1201(c), 1222, 1225(a)-(b). Once again, a derivative's fate is tied to the principal's: If the principal cannot enter the country, neither can her children (or spouse). See § 1153(d); 22 CFR § 40.1(a)(2). When, but only when, an alien with an immigrant visa is approved at the border does she finally become an LPR.5
  B
  All of this takes time-and often a lot of it. At the front end, many months may go by before USCIS approves the initial sponsoring petition. 6 On the back end, several additional months may elapse while a consular official considers the alien's visa application and schedules an interview.7 And the middle is the worst. After a sponsoring petition is approved but before a visa application can be filed, a family-sponsored immigrant may stand in line for years-or even decades-just waiting for an immigrant visa to become available. See, e.g., Dept. of State, Bureau of Consular Affairs, 9 Visa Bulletin, Immigrant Numbers for December 2013 (Nov. 8, 2013).
  And as the years tick by, young people grow up, and thereby endanger their immigration status. Remember that not all offspring, but only those under the age of 21 can qualify as an "immediate relative" of a U.S. citizen, or as the principal beneficiary of an LPR's F2A petition, or (most crucially here) as the derivative beneficiary of any family preference petition. See supra, at 2197, 2198. So an alien eligible to immigrate at the start of the process (when a sponsor files a petition) might not be so at the end (when an immigration official reviews his documents for admission). He may have "aged out" of his original immigration status by the simple passage of time.
  In 2002, Congress enacted the Child Status Protection Act (CSPA), 116 Stat. 927, to address the treatment of those once-but-no-longer-minor aliens. One section of the Act neatly eliminates the "aging out" problem for the offspring of U.S. citizens seeking to immigrate as "immediate relatives." Under that provision, the "determination of whether [such] an alien satisfies the [immigration law's] age requirement ... shall be made using [his] age" on the date the initial petition was filed. 8 U.S.C. § 1151(f)(1). The section thus halts the flow of time for that group of would-be immigrants: If an alien was young when a U.S. citizen sponsored his entry, then Peter Pan-like, he remains young throughout the immigration process.
  A different scheme-and one not nearly so limpid-applies to the offspring of LPRs and aliens who initially qualified as either principal beneficiaries of F2A petitions or derivative beneficiaries of any kind of family preference petition. Section 3 of the CSPA, now codified at 8 U.S.C. § 1153(h), contains three interlinked paragraphs that mitigate the "aging out" problem for those prospective immigrants. The first two are complex but, with some perseverance, comprehensible. The third-the key provision here-is through and through perplexing.8
  The first paragraph, § 1153(h)(1), contains a formula for calculating the age of an alien "[f]or purposes of subsections (a)(2)(A) and (d)"-that is, for any alien seeking an immigrant visa directly under F2A or as a derivative beneficiary of any preference category. The "determination of whether [such] an alien satisfies the [immigration law's] age requirement"-that is, counts as under 21-"shall be made using-
  "(A) the age of the alien on the date on which an immigrant visa number becomes available for such alien (or, in the case of [derivative beneficiaries], the date on which an immigrant visa number became available for the alien's parent) ...; reduced by
  "(B) the number of days in the period during which the applicable petition described in paragraph (2) was pending." § 1153(h)(1).
  The cross-referenced second paragraph, § 1153(h)(2), then explains that the "applicable petition" mentioned is the petition covering the given alien-so again, either an F2A petition filed on his own behalf or any petition extending to him as a derivative.
  Taken together, those two paragraphs prevent an alien from "aging out" because of-but only because of-bureaucratic delays: the time Government officials spend reviewing (or getting around to reviewing)
  paperwork at what we have called the front and back ends of the immigration process. See supra, at 2198 - 2199. The months that elapse before USCIS personnel approve a family preference petition ("the period during which the applicable petition described in paragraph (2) was pending") do not count against an alien in determining his statutory "age." Neither do the months a consular officer lets pass before adjudicating the alien's own visa application (the period after "an immigrant visa number becomes available for such alien (or ... [his] parent)"). But the time in between-the months or, more likely, years the alien spends simply waiting for a visa to become available-is not similarly excluded in calculating his age: Every day the alien stands in that line is a day he grows older, under the immigration laws no less than in life. And so derivative beneficiaries, as well as principal beneficiaries of F2A petitions, can still "age out"-in other words, turn 21, notwithstanding § 1153(h)(1)'s dual age adjustments-prior to receiving an opportunity to immigrate.
  What happens then (if anything) is the subject of § 1153(h)'s third paragraph-the provision at issue in this case. That paragraph states:
  "If the age of an alien is determined under paragraph (1) to be 21 years of age or older for the purposes of subsections (a)(2)(A) and (d) of this section, the alien's petition shall automatically be converted to the appropriate category and the alien shall retain the original priority date issued upon receipt of the original petition."
  The provision thus first references the aged-out beneficiaries of family preference petitions, and then directs immigration officials to do something whose meaning this opinion will further consider- i.e., "automatically convert" an alien's petition to an "appropriate category."
  The Board of Immigration Appeals (BIA) addressed the meaning of § 1153(h)(3) in Matter of Wang, 25 I. & N. Dec. 28 (2009); its interpretation there is what we review in this case. Wang was the principal beneficiary of an F4 petition that his sister, a U.S. citizen, filed in 1992. At that time, Wang's daughter was 10 years old, and thus qualified as a derivative beneficiary. But Wang waited in line for a visa for more than a decade, and by the time his priority date finally came up, his daughter had turned 22 (even after applying § 1153(h)(1)'s age-reduction formula). Wang thus obtained a visa for himself, boarded a plane alone, and entered the United States as an LPR. He then filed a new preference petition on his daughter's behalf-this one under F2B, the category for LPRs' adult sons and daughters. USCIS approved that petition, with a priority date corresponding to the date of Wang's filing. Wang contended that under § 1153(h)(3), his daughter was instead entitled to "retain the original priority date" given to his sister's old F4 petition, because that petition could "automatically be converted" to the F2B category.
  The Board rejected that argument. It explained that "the language of [§ 1153(h)(3) ] does not expressly state which petitions qualify for automatic conversion and retention of priority dates." Id., at 33. Given that "ambiguity," the BIA looked to the "recognized meaning" of "the phrase 'automatic conversion' " in immigration statutes and regulations-which it "presume[d]" Congress understood when enacting the CSPA. Id., at 33-35. "Historically," the BIA showed, that language applied only when a petition could move seamlessly from one family preference category to another-not when a new sponsor was needed to fit a beneficiary into a different category. Id., at 35. Some aged-out aliens' petitions could accomplish that maneuver, because the alien had a qualifying relationship with the original sponsor, and continued to do so upon aging out; in that event, the Board held, § 1153(h)(3) ensured that the alien would retain his original priority date. See id., at 34-35. But the F4 petition filed by Wang's sister could not "automatically be converted" in that way because Wang's daughter never had a qualifying relationship with the sponsor: "[N]o category exists for the niece of a United States citizen." Id., at 35-36. That is why Wang himself had to file a new petition on his daughter's behalf once she aged out and could no longer ride on his sibling status. The Board saw no evidence that Congress meant "to expand the use of the concept[ ] of automatic conversion" to reach such a case. Id., at 36. And the Board thought such an expansion unwarranted because it would allow aliens like Wang's daughter, who lacked any independent entitlement to a visa during the years her father spent standing on the F4 queue, to "cut[ ] in line ahead of others awaiting visas in other preference categories." Id., at 38.
  C
  The respondents in this case are similarly situated to Wang, and they seek the same relief. Each was once the principal beneficiary of either an F3 petition filed by a U.S. citizen parent or an F4 petition filed by a U.S. citizen sibling. Each also has a son or daughter who, on the date of filing, was under 21 and thus qualified as a derivative beneficiary of the petition. But as was true of Wang's daughter, the respondents' offspring had all turned 21 (even accounting for § 1153(h)(1)'s age adjustments) by the time visas became available. Accordingly, the respondents immigrated to the United States alone and, as new LPRs, filed F2B petitions for their sons and daughters. Each argued that under § 1153(h)(3), those petitions should get the same priority date as the original F3 and F4 petitions once had. USCIS instead gave the new F2B petitions current priority dates, meaning that the sons and daughters could not leapfrog over others in the F2B line.
  This case began as two separate suits, one joining many individual plaintiffs and the other certified as a class action. In each suit, the District Court deferred to the BIA's interpretation of § 1153(h)(3) in Wang, and accordingly granted summary judgment to the Government. See Zhang v. Napolitano, 663 F.Supp.2d 913, 919 (C.D.Cal.2009); Costelo v. Chertoff, No. SA08-00688, 2009 WL 4030516 (C.D.Cal., Nov. 10, 2009). After consolidating the two cases on appeal, a panel of the Ninth Circuit affirmed: Like the lower courts, it found § 1153(h)(3) ambiguous and acceded to the BIA's construction. 656 F.3d 954, 965-966 (2011). The Ninth Circuit then granted rehearing en banc and reversed in a 6-to-5 decision. 695 F.3d 1003 (2012). The majority concluded that "the plain language of the CSPA unambiguously grants automatic conversion and priority date retention to [all] aged-out derivative beneficiaries," and that the Board's contrary conclusion "is not entitled to deference." Id., at 1006.
  We granted certiorari, 570 U.S. ----, 133 S.Ct. 2853, 186 L.Ed.2d 907 (2013), to resolve a Circuit split on the meaning of § 1153(h)(3), 9 and we now reverse the Ninth Circuit's decision.
  II
  Principles of Chevron deference apply when the BIA interprets the immigration laws. See Chevron U.S.A. Inc. v. Natural Resources Defense Council, Inc., 467 U.S. 837, 842-844, 104 S.Ct. 2778, 81 L.Ed.2d 694 (1984); INS v. Aguirre-Aguirre, 526 U.S. 415, 424-425, 119 S.Ct. 1439, 143 L.Ed.2d 590 (1999). Indeed, "judicial deference to the Executive Branch is especially appropriate in the immigration context," where decisions about a complex statutory scheme often implicate foreign relations. Id., at 425, 119 S.Ct. 1439. (Those hardy readers who have made it this far will surely agree with the "complexity" point.) Under Chevron, the statute's plain meaning controls, whatever the Board might have to say. See 467 U.S., at 842-843, 104 S.Ct. 2778. But if the law does not speak clearly to the question at issue, a court must defer to the Board's reasonable interpretation, rather than substitute its own reading. Id., at 844, 104 S.Ct. 2778.
  And § 1153(h)(3) does not speak unambiguously to the issue here-or more precisely put, it addresses that issue in divergent ways. We might call the provision Janus-faced. Its first half looks in one direction, toward the sweeping relief the respondents propose, which would reach every aged-out beneficiary of a family preference petition. But as the BIA recognized, and we will further explain, the section's second half looks another way, toward a remedy that can apply to only a subset of those beneficiaries-and one not including the respondents' offspring. The two faces of the statute do not easily cohere with each other: Read either most naturally, and the other appears to mean not what it says. That internal tension makes possible alternative reasonable constructions, bringing into correspondence in one way or another the section's different parts. And when that is so, Chevron dictates that a court defer to the agency's choice-here, to the Board's expert judgment about which interpretation fits best with, and makes most sense of, the statutory scheme.
  Begin by reading the statute from the top-the part favoring the respondents. Section 1153(h)(3)'s first clause-"If the age of an alien is determined under paragraph (1) to be 21 years of age or older for the purposes of subsections (a)(2)(A) and (d)"-states a condition that every aged-out beneficiary of a preference petition satisfies. That is because all those beneficiaries have had their ages "determined under paragraph (1)" (and have come up wanting): Recall that the age formula of § 1153(h)(1) applies to each alien child who originally qualified (under "subsections (a)(2)(A) and (d)") as the principal beneficiary of an F2A petition or the derivative beneficiary of any family preference petition. On its own, then, § 1153(h)(3)'s opening clause encompasses the respondents' sons and daughters, along with every other once-young beneficiary of a family preference petition now on the wrong side of 21. If the next phrase said something like "the alien shall be treated as though still a minor" (much as the CSPA did to ensure U.S. citizens' children, qualifying as "immediate relatives," would stay forever young, see supra, at 2199 - 2200), all those aged-out beneficiaries would prevail in this case.
  But read on, because § 1153(h)(3)'s second clause instead prescribes a remedy containing its own limitation on the eligible class of recipients. "[T]he alien's petition," that part provides, "shall automatically be converted to the appropriate category and the alien shall retain the original priority date." That statement directs immigration officials to take the initial petition benefitting an alien child, and now that he has turned 21, "convert[ ]" that same petition from a category for children to an "appropriate category" for adults (while letting him keep the old priority date). The "conversion," in other words, is merely from one category to another; it does not entail any change in the petition, including its sponsor, let alone any new filing. And more, that category shift is to be "automatic"-that is, one involving no additional decisions, contingencies, or delays. See, e.g., Random House Webster's Unabridged Dictionary 140 (2d ed. 2001) (defining "automatic" as "having the capability of starting, operating, moving, etc., independently"); The American Heritage Dictionary 122 (4th ed. 2000) ("[a]cting or operating in a manner essentially independent of external influence"). The operation described is, then, a mechanical cut-and-paste job-moving a petition, without any substantive alteration, from one (no-longer-appropriate, child-based) category to another (now-appropriate, adult) compartment. And so the aliens who may benefit from § 1153(h)(3)'s back half are only those for whom that procedure is possible. The clause offers relief not to every aged-out beneficiary, but just to those covered by petitions that can roll over, seamlessly and promptly, into a category for adult relatives.
  That understanding of § 1153(h)(3)'s "automatic conversion" language matches the exclusive way immigration law used the term when Congress enacted the CSPA. For many years before then (as today), a regulation entitled "Automatic conversion of preference classification" instructed immigration officials to change the preference category of a petition's principal beneficiary when either his or his sponsor's status changed in specified ways. See 8 CFR §§ 204.2(i)(1)-(3) (2002). For example, the regulation provided that when a U.S. citizen's child aged out, his "immediate relative" petition converted to an F1 petition, with his original priority date left intact. See § 204.2(i)(2). Similarly, when a U.S. citizen's adult son married, his original petition migrated from F1 to F3, see § 204.2(i)(1)(i); when, conversely, such a person divorced, his petition converted from F3 to F1, see § 204.2(i)(1)(iii); and when a minor child's LPR parent became a citizen, his F2A petition became an "immediate relative" petition, see § 204.2(i)(3)-all again with their original priority dates. Most notable here, what all of those authorized changes had in common was that they could occur without any change in the petitioner's identity, or otherwise in the petition's content. In each circumstance, the "automatic conversion" entailed nothing more than picking up the petition from one category and dropping it into another for which the alien now qualified.10
  Congress used the word "conversion" (even without the modifier "automatic") in the identical way in two other sections of the CSPA. See Law v. Siegel, 571 U.S. ----, ----, 134 S.Ct. 1188, 1195, 188 L.Ed.2d 146 (2014) ("[W]ords repeated in different parts of the same statute generally have the same meaning"). Section 2 refers to occasions on which, by virtue of the above-described regulation, a petition "converted" from F2A to the "immediate relative" category because of the sponsor parent's naturalization, or from the F3 to the F1 box because of the beneficiary's divorce. 8 U.S.C. §§ 1151(f)(2), (3). Then, in § 6, Congress authorized an additional conversion of the same nature: It directed that when an LPR parent-sponsor naturalizes, the petition he has filed for his adult son or daughter "shall be converted," unless the beneficiary objects, from the F2B to the F1 compartment-again with the original priority date unchanged. 8 U.S.C. §§ 1154(k)(1)-(3). (That opt-out mechanism itself underscores the otherwise mechanical nature of the conversion.) Once again, in those cases, all that is involved is a recategorization-moving the same petition, filed by the same petitioner, from one preference classification to another, so as to reflect a change in either the alien's or his sponsor's status. In the rest of the CSPA, as in the prior immigration regulation, that is what "conversion" means.
  And if the term meant more than that in § 1153(h)(3), it would undermine the family preference system's core premise: that each immigrant must have a qualified sponsor. Consider the alternative addressed in Wang-if "automatic conversion" were also to encompass the substitution of a new petitioner for the old one, to make sure the aged-out alien's petition fits into a new preference category. In a case like Wang, recall, the original sponsor does not have a legally recognized relationship with the aged-out derivative beneficiary (they are aunt and niece); accordingly, the derivative's father-the old principal beneficiary-must be swapped in as the petitioner to enable his daughter to immigrate. But what if, at that point, the father is in no position to sponsor his daughter? Suppose he decided in the end not to immigrate, or failed to pass border inspection, or died in the meanwhile. Or suppose he entered the country, but cannot sponsor a relative's visa because he lacks adequate proof of parentage or committed a disqualifying crime. See § 1154(a)(1)(B)(i)(II); 8 CFR § 204.2(d)(2); supra, at 2197. Or suppose he does not want to-or simply cannot-undertake the significant financial obligations that the law imposes on someone petitioning for an alien's admission. See 8 U.S.C. §§ 1183a(a)(1)(A), (f)(1)(D); supra, at 2198. Immigration officials cannot assume away all those potential barriers to entry: That would run counter to the family preference system's insistence that a qualified and willing sponsor back every immigrant visa. See §§ 1154(a)-(b). But neither can they easily, or perhaps at all, figure out whether such a sponsor exists unless he files and USCIS approves a new petition-the very thing § 1153(h)(3) says is not required.
  Indeed, in cases like Wang, the problem is broader: Under the statute's most natural reading, a new qualified sponsor will hardly ever exist at the moment the petition is to be "converted." Section 1153(h)(3), to be sure, does not explicitly identify that point in time. But § 1153(h)(1) specifies the date on which a derivative beneficiary is deemed to have either aged out or not: It is "the date on which an immigrant visa number became available for the alien's parent." See §§ 1153(h)(1)(A)-(B). Because that statutory aging out is the one and only thing that triggers automatic conversion for eligible aliens, the date of conversion is best viewed as the same. That reading, moreover, comports with the "automatic conversion" regulation on which Congress drew in enacting the CSPA, see supra, at 2204 - 2205: The rule authorizes conversions "upon" or "as of the date" of the relevant change in the alien's status (including turning 21)-regardless when USCIS may receive notice of the change. 8 CFR § 204.2(i); but cf. post, at 2224 (SOTOMAYOR, J., dissenting) (wrongly stating that under that rule conversion occurs upon the agency's receipt of proof of the change). But on that date, no new petitioner will be ready to step into the old one's shoes if such a substitution is needed to fit an aged-out beneficiary into a different category. The beneficiary's parent, on the day a "visa number became available," cannot yet be an LPR or citizen; by definition, she has just become eligible to apply for a visa, and faces a wait of at least several months before she can sponsor an alien herself. Nor, except in a trivial number of cases, is any hitherto unidentified person likely to have a legally recognized relationship to the alien. So if an aged-out beneficiary has lost his qualifying connection to the original petitioner, no conversion to an "appropriate category" can take place at the requisite time. As long as immigration law demands some valid sponsor, § 1153(h)(3) cannot give such an alien the designated relief.
  On the above account-in which conversion entails a simple reslotting of an original petition into a now-appropriate category-§ 1153(h)(3)'s back half provides a remedy to two groups of aged-out beneficiaries. First, any child who was the principal beneficiary of an F2A petition (filed by an LPR parent on his behalf) can take advantage of that clause after turning 21. He is, upon aging out, the adult son of the same LPR who sponsored him as a child; his petition can therefore be moved seamlessly-without the slightest alteration or delay-into the F2B category. Second, any child who was the derivative beneficiary of an F2A petition (filed by an LPR on his spouse's behalf) can similarly claim relief, provided that under the statute, he is not just the spouse's but also the petitioner's child.11 Such an alien is identically situated to the aged-out principal beneficiary of an F2A petition; indeed, for the price of another filing fee, he could just as easily have been named a principal himself. He too is now the adult son of the original LPR petitioner, and his petition can also be instantly relabeled an F2B petition, without any need to substitute a new sponsor or make other revisions. In each case, the alien had a qualifying relationship before he was 21 and retains it afterward; all that must be changed is the label affixed to his petition. 12
  In contrast, as the Board held in Wang, the aged-out derivative beneficiaries of the other family preference categories-like the sons and daughters of the respondents here-cannot qualify for "automatic conversion." Recall that the respondents themselves were principal beneficiaries of F3 and F4 petitions; their children, when under 21, counted as derivatives, but lacked any qualifying preference relationship of their own. The F3 derivatives were the petitioners' grandsons and granddaughters; the F4 derivatives their nephews and nieces; and none of those are relationships Congress has recognized as warranting a family preference. See 8 U.S.C. §§ 1153(a)(3)-(4). Now that the respondents' children have turned 21, and they can no longer ride on their parents' coattails, that lack of independent eligibility makes a difference. For them, unlike for the F2A beneficiaries, it is impossible simply to slide the original petitions from a (no-longer-appropriate) child category to a (now-appropriate) adult one. To fit into a new category, those aged-out derivatives, like Wang's daughter, must have new sponsors-and for all the reasons already stated, that need means they cannot benefit from "automatic conversion."
  All that said, we hold only that § 1153(h)(3) permits-not that it requires-the Board's decision to so distinguish among aged-out beneficiaries. That is because, as we explained earlier, the two halves of § 1153(h)(3) face in different directions. See supra, at 2203. Section 1153(h)(3)'s first part-its conditional phrase-encompasses every aged-out beneficiary of a family preference petition, and thus points toward broad-based relief. But as just shown, § 1153(h)(3)'s second part-its remedial prescription-applies only to a narrower class of beneficiaries: those aliens who naturally qualify for (and so can be "automatically converted" to) a new preference classification when they age out. Were there an interpretation that gave each clause full effect, the Board would have been required to adopt it. But the ambiguity those ill-fitting clauses create instead left the Board with a choice-essentially of how to reconcile the statute's different commands. The Board, recognizing the need to make that call, opted to abide by the inherent limits of § 1153(h)(3)'s remedial clause, rather than go beyond those limits so as to match the sweep of the section's initial condition. On the Board's reasoned view, the only beneficiaries entitled to statutory relief are those capable of obtaining the remedy designated. When an agency thus resolves statutory tension, ordinary principles of administrative deference require us to defer. See National Assn. of Home Builders v. Defenders of Wildlife, 551 U.S. 644, 666, 127 S.Ct. 2518, 168 L.Ed.2d 467 (2007) (When a statutory scheme contains "a fundamental ambiguity" arising from "the differing mandates" of two provisions, "it is appropriate to look to the implementing agency's expert interpretation" to determine which "must give way").
  III
  The respondents urge us to overturn the Board's judgment for three independent reasons. First, and principally, they take issue with the Board's-and now our-view of the limits associated with "automatic conversion": They argue that every aged-out beneficiary's petition can "automatically be converted" to an "appropriate category," and that the two halves of § 1153(h)(3) are thus reconcilable. Second, the respondents contend that even if "automatic conversion" does not extend so far, § 1153(h)(3) separately entitles each such beneficiary to the benefit of his original petition's priority date. And third, they claim that the Board's way of resolving whatever ambiguity inheres in § 1153(h)(3) is arbitrary and capricious. The dissenting opinion reiterates the first two arguments, though with slight variation and in opposite order, while forgoing the third. See post, at 2221 - 2227 (opinion of SOTOMAYOR, J.) (hereinafter the dissent). We find none of the contentions persuasive.
  A
  The respondents (and the dissent) initially aver that every aged-out beneficiary (including their own sons and daughters) can "automatically be converted" to an "appropriate" immigration category, if only immigration officials try hard enough. The Government, in the respondents' view, can accomplish that feat by substituting new sponsors for old ones, and by "managing the timing" of every conversion to ensure such a new petitioner exists on the relevant date. Brief for Respondents 33. And because, the respondents say, it is thus possible to align the two halves of § 1153(h)(3)-even if through multiple administrative maneuvers-immigration officials are under an obligation to do so. We disagree, for reasons that should sound familiar: Several are the same as those we have just given for upholding the Board's interpretation. But still, we walk through the respondents' argument step-by-step, to show how far it departs from any ordinary understanding of "automatic conversion."
  The first (and necessary) premise of that argument does not augur well for the remainder: It is the view that the "automatic conversion" procedure permits a change in the petitioner's identity. According to the respondents, the aged-out beneficiaries' parents, upon becoming LPRs, can be subbed in for the original sponsors ( i.e., the beneficiaries' grandparents, aunts, and uncles), and the petitions then converted to the F2B category. But as we have shown, the "automatic conversion" language-as most naturally read and as long used throughout immigration law-contemplates merely moving a petition into a new and valid category, not changing its most essential feature. See supra, at 2203 - 2205. That alone defeats the respondents' position.
  And a further problem follows-this one concerning the date of automatic conversion. The respondents need that date to come at a time when the derivative beneficiaries' parents (the substitute petitioners) are already living in the United States as LPRs; otherwise, the petitions could not qualify for the F2B box. In an attempt to make that possible, the respondents propose that conversion be viewed as taking place when "the derivative beneficiary's visa ... application is adjudicated." Brief for Respondents 29. But as we have (again) demonstrated, the statute is best read as establishing a different date: that "on which an immigrant visa number became available for the alien's parent"-when, by definition, the parent is not yet an LPR. § 1153(h)(1); see supra, at 2205 - 2206. That is the moment when a derivative ages out, which is the single change conversion reflects. By contrast, the respondents' suggested date has no connection to that metamorphosis; the date of adjudication is merely when an immigration official later discovers that a child has turned 21. And that date is itself fortuitous, reflecting no more than when an immigration officer got around to reviewing a visa application: The possibility of conversion would thus depend on bureaucratic vagaries attending the visa process. So the respondents' mistaken view of the timing of conversion is another off-ramp from their argument.13
  Yet there is more-because even after substituting a new petitioner and delaying the conversion date in a way the statute does not contemplate, the respondents must propose yet further fixes to make "automatic" conversion work for their sons and daughters. The respondents' next problem is that even on the conversion date they propose, most of them (and other derivatives' parents) were not yet LPRs, and so could not possibly be sponsors. In the ordinary course, principal and derivative beneficiaries living abroad apply for their visas at the same time and go to the consulate together for back-to-back interviews. See supra, at 2198. And even if the parent is approved first, that alone does not make her an LPR; she still must come to this country, demonstrate her continued eligibility, and pass an inspection. See ibid. Thus, the respondents must recommend changes to the visa process to get the timing to work-essentially, administrative juggling to hold off the derivative beneficiary's visa adjudication until his parent has become an LPR. In particular, they suggest that the consular official defer the derivative's interview, or that the official nominally "reject the application" and then instruct the derivative to "reapply after the principal beneficiary immigrates." Brief for Respondents 30. But the need for that choreography (which, in any event, few if any of the respondents conformed to) renders the conversion process only less "automatic," because now it requires special intervention, purposeful delay, and deviation from standard administrative practice. Conversion has become not a machine that would go of itself, but a process painstakingly managed.
  And after all this fancy footwork, the respondents' scheme still cannot succeed, because however long a visa adjudication is postponed, a derivative's parent may never become able to sponsor a relative's visa-and immigration officials cannot practicably tell whether a given parent has done so. We have noted before the potential impediments to serving as a petitioner-including that a parent may not immigrate, may not qualify as a sponsor, or may not be able to provide the requisite financial support. See supra, at 2205 - 2206. The respondents offer no way to deal with those many contingencies. Require the parent to submit a new petition? But the entire point of automatic conversion (as the respondents themselves agree) is to obviate the need for such a document. See Brief for Respondents 30, 42. Investigate the parent's eligibility in some other way? But even were that possible (which we doubt) such an inquiry would not square with the essential idea of an automatic process. Disregard the possibility that no legal sponsor exists? But then visas would go, inevitably and not infrequently, to ineligible aliens. And so the workarounds have well and truly run out on the respondents' argument. 14
  That leaves us with the same statutory inconsistency with which we began. Having followed each step of the respondents' resourceful (if Rube Goldbergish) argument, we still see no way to apply the concept of automatic conversion to the respondents' children and others like them. And that means we continue to face a statute whose halves do not correspond to each other-giving rise to an ambiguity that calls for Chevron deference.
  B
  The respondents, however, have another idea for reconciling § 1153(h)(3)'s front and back parts (and this back-up claim becomes the dissent's principal argument). Recall that the section's remedial clause instructs that "the alien's petition shall automatically be converted to the appropriate category and the alien shall retain the original priority date issued upon receipt of the original petition." The respondents (and the dissent) ask us to read the italicized language as conferring a benefit wholly independent of automatic conversion. On that view, aged-out derivatives, even though ineligible for conversion, could "retain the[ir] original priority date[s]" if their parents file a new petition (as the respondents in fact did here "as a protective matter," Tr. of Oral Arg. 55). And then, everyone encompassed in § 1153(h)(3)'s first clause would get at least some form of relief (even if not both forms) from the section's second. For this argument, the respondents principally rely on the word "and": "Where the word 'and' connects two" phrases as in § 1153(h)(3)'s back half, the respondents contend, those terms "operate independently." Brief for Respondents 39; see post, at 2221.
  But the conjunction "and" does not necessarily disjoin two phrases in the way the respondents say. In some sentences, no doubt, the respondents have a point. They use as their primary example: "[I]f the boat takes on water, then you shall operate the bilge pump and you shall distribute life jackets." Brief for Respondents 39; see also post, at 2221 (offering further examples). We agree that "you shall distribute life jackets" functions in that sentence as an independent command. But we can come up with many paired dictates in which the second is conditional on the first. "If the price is reasonable, buy two tickets and save a receipt." "If you have time this summer, read this book and give me a report." Or, shades of this case: "If your cell-phone contract expires, buy a new phone and keep the old number." 15 In each case, the second command functions only once the first is accomplished. Whether "and" works in that way or in the respondents' depends, like many questions of usage, on the context. See, e.g., Caraco Pharmaceutical Laboratories, Ltd. v. Novo Nordisk A/S, 566 U.S. ----, ----, 132 S.Ct. 1670, ----, 182 L.Ed.2d 678 (2012).
  Here, we think, context compels the Board's view that the instructions work in tandem. The first phrase instructs immigration officials to convert a petition (when an "appropriate category" exists); the next clarifies that such a converted petition will retain the original priority date, rather than receive a new one corresponding to the date of conversion. That reading comports with the way retention figures in other statutory and regulatory provisions respecting "conversions"; there too, retention of a priority date is conditional on a conversion occurring. See 8 U.S.C. §§ 1154(k)(1)-(3); 8 CFR § 204.2(i); supra, at 2204. The respondents wish to unhook the "retention" phrase from that mooring, and use it to explain what will attend a different event-that is, the filing of a new petition. But that is to make "retention" conditional on something the statute nowhere mentions-a highly improbable thing for Congress to have done. (If, once again, a teacher says to "read this book and give me a report," no one would think he wants a report on some unidentified subject.) And indeed, the respondents' and dissent's own examples prove this point: In not a single one of their proffered sentences is the second command contingent on the occurrence of some additional, unstated event, as it would have to be under the respondents' construction of § 1153(h)(3); rather, each such command ( e.g., "distribute life jackets") flows directly from the stated condition ( e.g., "if the boat takes on water"). So by far the more natural understanding of § 1153(h)(3)'s text is that retention follows conversion, and nothing else.
  The respondents' contrary view would also engender unusual results, introducing uncertainty into the immigration system's operation and thus interfering with statutory goals. Were their theory correct, an aged-out alien could hold on to a priority date for years or even decades while waiting for a relative to file a new petition. Even if that filing happened, say, 20 years after the alien aged out, the alien could take out his priority-date token, and assert a right to spring to the front of any visa line. At that point, USCIS could well have a hard time confirming the old priority date, in part because the names of derivative beneficiaries need not be listed on a visa petition. And the possibility of such leap-frogging from many years past would impede USCIS's publication of accurate waiting times. As far as we know, immigration law nowhere else allows an alien to keep in his pocket a priority date untethered to any existing valid petition. Without some clearer statement, we cannot conclude Congress intended here to create such a free-floating, open-ended entitlement to a defunct petition's priority date. See Wang, 25 I. & N. Dec., at 36.16
  C
  Finally, the respondents contend that even if § 1153(h)(3) points at once in two directions-toward a broader scope in its first half and a narrower one in its second-the BIA acted unreasonably in choosing the more restrictive reading. In their view, the Board has offered no valid reason, consistent with "the purposes and concerns of the immigration laws," to treat their own sons and daughters less favorably than aliens who were principal and derivative beneficiaries of F2A petitions. Brief for Respondents 47. Indeed, the respondents suggest that the BIA, "for its own unfathomable reasons, disapproves of Congress's decision to allow any aged-out" aliens to get relief, and has thus "limited [§ 1153(h)(3) ] to as few derivative beneficiaries as possible." Id., at 55.
  We cannot agree. At the least, the Board's interpretation has administrative simplicity to recommend it. Under that view, immigration authorities need only perform the kind of straightforward ( i.e., "automatic") conversion they have done for decades-moving a petition from one box to another to reflect a given status change like aging out. See Wang, 25 I. & N. Dec., at 36. The respondents, as we have shown, would transform conversion into a managed, multi-stage process, requiring immigration and consular officials around the world to sequence and delay every aged-out alien's visa adjudication until they are able to confirm that one of his parents had become a qualifying and willing F2B petitioner. And according to the Government's (incomplete) statistics, that would have to happen in, at a minimum, tens of thousands of cases every year. See Reply Brief 18, n. 13.
  Still more important, the Board offered a cogent argument, reflecting statutory purposes, for distinguishing between aged-out beneficiaries of F2A petitions and the respondents' sons and daughters. See Wang, 25 I. & N. Dec., at 38. As earlier explained, the F2A beneficiaries have all had a qualifying relationship with an LPR for the entire period they have waited in line- i.e., since their original priority dates. See supra, at 2205 - 2206. That means that when immigration authorities convert their petitions, they will enter the F2B line at the same place as others who have had a comparable relationship for an equal time. The conversion thus fits with the immigration law's basic first-come-first-served rule. See 8 U.S.C. § 1153(e); supra, at 2197. By contrast, the derivative beneficiaries of F3 and F4 petitions, like the respondents' sons and daughters, lacked any qualifying relationship with a citizen or LPR during the period they waited in line. See supra, at 2206 - 2207. They were, instead, the grandchildren, nieces, or nephews of citizens, and those relationships did not independently entitle them to visas. If such aliens received relief under § 1153(h)(3), they would jump over thousands of others in the F2B line who had a qualifying relationship with an LPR for a far longer time. That displacement would, the Board reasonably found, scramble the priority order Congress prescribed.
  The argument to the contrary assumes that the respondents' sons and daughters should "receive credit" for all the time the respondents themselves stood in line. Brief for Respondents 50. But first, the time the respondents spent waiting for a visa may diverge substantially from the time their children did. Suppose, for example, that one of the respondents had stood in the F4 queue for 15 years, and with just 4 years to go, married someone with a 17-year-old son. Under the respondents' reading, that derivative beneficiary, after aging out, would get the full benefit of his new parent's wait, and so displace many thousands of aliens who (unlike him) had stood in an immigration queue for nearly two decades. And second, even when the derivative qualified as such for all the time his parent stood in line, his status throughout that period hinged on his being that parent's minor child. If his parent had obtained a visa before he aged out, he would have been eligible for a visa too, because the law does not demand that a prospective immigrant abandon a minor child. But if the parent had died while waiting for a visa, or had been found ineligible, or had decided not to immigrate after all, the derivative would have gotten nothing for the time spent in line. See supra, at 2198 - 2199. Similarly, the Board could reasonably conclude, he should not receive credit for his parent's wait when he has become old enough to live independently. In the unavoidably zero-sum world of allocating a limited number of visas, the Board could decide that he belongs behind any alien who has had a lengthier stand-alone entitlement to immigrate.
  IV
  This is the kind of case Chevron was built for. Whatever Congress might have meant in enacting § 1153(h)(3), it failed to speak clearly. Confronted with a self-contradictory, ambiguous provision in a complex statutory scheme, the Board chose a textually reasonable construction consonant with its view of the purposes and policies underlying immigration law. Were we to overturn the Board in that circumstance, we would assume as our own the responsible and expert agency's role. We decline that path, and defer to the Board.
  We therefore reverse the judgment of the Ninth Circuit and remand the case for further proceedings consistent with this opinion.
  It is so ordered.
  Chief Justice ROBERTS, with whom Justice SCALIA joins, concurring in the judgment.
  I agree with much of the plurality's opinion and with its conclusion that the Board of Immigration Appeals reasonably interpreted 8 U.S.C. § 1153(h)(3). I write separately because I take a different view of what makes this provision "ambiguous" under Chevron U.S.A. Inc. v. Natural Resources Defense Council, Inc., 467 U.S. 837, 843, 104 S.Ct. 2778, 81 L.Ed.2d 694 (1984).
  As the plurality reads section 1153(h)(3), the statute's two clauses address the issue before the Court "in divergent ways" and "do not easily cohere with each other." Ante, at 2203. For the plurality, the first clause looks "toward the sweeping relief the respondents propose, which would reach every aged-out beneficiary of a family preference petition," while the second clause offers narrower relief that can help "only a subset of those beneficiaries." Ibid. Such "ill-fitting clauses," the plurality says, "left the Board with a choice-essentially of how to reconcile the statute's different commands." Ante, at 2207.
  To the extent the plurality's opinion could be read to suggest that deference is warranted because of a direct conflict between these clauses, that is wrong. Courts defer to an agency's reasonable construction of an ambiguous statute because we presume that Congress intended to assign responsibility to resolve the ambiguity to the agency. Chevron, supra, at 843-844, 104 S.Ct. 2778. But when Congress assigns to an agency the responsibility for deciding whether a particular group should get relief, it does not do so by simultaneously saying that the group should and that it should not. Direct conflict is not ambiguity, and the resolution of such a conflict is not statutory construction but legislative choice. Chevron is not a license for an agency to repair a statute that does not make sense.1
  I see no conflict, or even "internal tension," ante, at 2203, in section 1153(h)(3). See FDA v. Brown & Williamson Tobacco Corp., 529 U.S. 120, 133, 120 S.Ct. 1291, 146 L.Ed.2d 121 (2000) (we must "interpret the statute 'as a symmetrical and coherent regulatory scheme,' and 'fit, if possible, all parts into a[ ] harmonious whole' " (citation omitted)).
  The statute reads:
  "If the age of an alien is determined under [section 1153(h)(1) ] to be 21 years of age or older for the purposes of subsections (a)(2)(A) and (d) of this section, the alien's petition shall automatically be converted to the appropriate category and the alien shall retain the original priority date issued upon receipt of the original petition." § 1153(h)(3).
  The first clause states a condition-one that beneficiaries from any preference category can meet-and thereby defines the persons potentially affected by this provision. But the clause does not grant anything to anyone. I disagree with the plurality that the first clause "points toward broad-based relief," ante, at 2207, because I do not think the first clause points toward any relief at all.2
  Imagine a provision of the Tax Code that read: "If a student is determined to be enrolled at an accredited university, the student's cost of off-campus housing shall be deductible on her tax return." It would be immediately apparent from that provision that an enrolled student who lives on campus is not entitled to the deduction, even though the student falls within the conditional first clause. And yet no one would describe the two clauses as being in tension. If the Internal Revenue Service then interpreted the term "cost of off-campus housing" to exclude payments by a student who rents a home from his parents, a court would determine whether that interpretation was reasonable. The same is true in this case.3
  The particular benefit provided by section 1153(h)(3) is found exclusively in the second clause-the only operative provision. There we are told what an aged-out beneficiary (from whatever preference category) is entitled to: His petition "shall automatically be converted to the appropriate category and the alien shall retain the original priority date." § 1153(h)(3). But automatic conversion is not possible for every beneficiary in every preference category, as the plurality convincingly demonstrates. Ante, at 2203 - 2206. Automatic conversion requires, at minimum, that the beneficiary have his own sponsor, who demonstrates that he is eligible to act as a sponsor, and who commits to providing financial support for the beneficiary. Ante, at 2205. Some aged-out children will not meet those prerequisites, and they cannot benefit from automatic conversion even under respondents' interpretation of the statute.4
  Beyond those requirements, however, Congress did not speak clearly to which petitions can "automatically be converted." § 1153(h)(3). Whatever other interpretations of that provision might be possible, it was reasonable, for the reasons explained by the plurality, for the Board to interpret section 1153(h)(3) to provide relief only to a child who was a principal or derivative beneficiary of an F2A petition. That interpretation is consistent with the ordinary meaning of the statutory terms, with the established meaning of automatic conversion in immigration law, and with the structure of the family-based immigration system. Ante, at 2203 - 2206. It also avoids the problems that would flow from respondents' proposed alternative interpretations, including the suggestion that retention of the original priority date provides a benefit wholly separate from automatic conversion. Ante, at 2205 - 2206, 2207 - 2208.
  I concur in the judgment.
choices: stay, petition, or motion granted affirmed (includes modified) reversed reversed and remanded vacated and remanded affirmed and reversed (or vacated) in part affirmed and reversed (or vacated) in part and remanded vacated petition denied or appeal dismissed certification to or from a lower court no disposition