opinion: BABBITT, SECRETARY OF INTERIOR, et al. v. SWEET HOME CHAPTER OF COMMUNITIES FOR A GREAT OREGON et al.
  No. 94-859.
  Argued April 17, 1995 —
  Decided June 29, 1995
  Stevens, J., delivered the opinion of the Court, in which O’Connor, Kennedy, Souter, Ginsburg, and Breyer, JJ., joined. O’Connor, J., filed a concurring opinion, post, p. 708. Scalia, J., filed a dissenting opinion, in which Rehnquist, C. J., and Thomas, J., joined, post, p. 714.
  Deputy Solicitor General Kneedler argued the cause for petitioners. With him on the briefs were Solicitor General Days, Assistant Attorney General Schiffer, Beth S. Brink-mann, Martin W. Matzen, Ellen J. Durkee, and Jean E. Williams.
  John A. Macleod argued the cause for respondents. With him on the brief were Steven P. Quarles, Clifton S. Elgar-ten, Thomas R. Lundquist, and William R. Murray.
  Briefs of amici curiae urging reversal were filed for the Environmental Law Committee of the Association of the Bar of the City of New York by Brent L. Brandenburg; for Friends of Animals, Inc., by Herman Kaufman; for the National Wildlife Federation et al. by Patti A Goldman and Todd D. Trice; and for Scientist John Cairns, Jr., et al. by Wm. Robert Irvin, Timothy Eichenberg, and Patrick A Parenteau.
  Briefs of amici curiae urging affirmance were filed for the State of Arizona ex rel. M. J. Hassel, Arizona State Land Commissioner, et al. by Grant Woods, Attorney General of Arizona, Mary Mangotich Grier, Assistant Attorney General, and Gale A Norton, Attorney General of Colorado; for the State of California et al. by Daniel Lungren, Attorney General of California, Roderick E. Walston, Chief Assistant Attorney General, Charles W. Getz TV, Assistant Attorney General, and Linus Ma-souredis, Deputy Attorney General, and for the Attorneys General for their respective States as follows: Carla J. Stovall of Kansas, Don Sten-berg of Nebraska, and Jan Graham of Utah; for the State of Texas by Dan Morales, Attorney General, Jorge Vega, First Assistant Attorney General, Javier Aguilar and Sam Goodhope, Special Assistant Attorneys General, and Paul Terrill and Eugene Montes, Assistant Attorneys General; for the American Farm Bureau Federation et al. by Timothy S. Bishop, Michael F. Rosenblum, John J. Rademacher, Richard L. Krause, Nancy N. McDonough, Carolyn S. Richardson, Douglas G. Caroom, and Sydney W. Falk, Jr.; for Anderson & Middleton Logging Co., Inc., by Mark C. Kutzick and J. J. Leary, Jr.; for Cargill, Inc., by Louis F. Claiborne, Edgar B. Washburn, and David Ivester; for the Chamber of Commerce of the United States of America et al. by Virginia S. Albrecht, Robin S. Conrad, Ted R. Brown, and Ralph W. Holmen; for the Competitive Enterprise Institute by Sam Kazman; for the Davis Mountains Trans-Pecos Heritage Association et al. by Nancie G. Marzulla; for the Florida Legal Foundation et al. by Michael L. Rosen and G. Stephen Parker; for the Institute for Justice by Richard A Epstein, William H. Mellor III, and Clint Bolick; for the National Association of Home Builders et al. by D. Barton Doyle; for the National Cattlemen’s Association et al. by Roger J. Marzulla, Michael T. Lempres, and William G. Myers III; for the Mountain States Legal Foundation et al. by William Perry Pendley; for the Pacific Legal Foundation et al. by Robin L. Rivett; for the State Water Contractors et al. by Gregory K. Wilkinson, Eric L. Garner, Thomas W. Birmingham, and Stuart L. Somach; for the Washington Legal Foundation et al. by Albert Gidari, Daniel J. Popeo, and Paul D. Kamenar; and for Congressman Bill Baker et al. by Virginia S. Albrecht.
  Briefs of amici curiae were filed for the Nationwide Public Projects Coalition et al. by Lawrence R. Liebesman, Kenneth S. Kamlet, and Duane J. Desiderio; and for the Navajo Nation et al. by Scott B. McElroy, Lester K. Taylor, Daniel H. Israel, and Stanley Pollack.
  Justice Stevens
  delivered the opinion of the Court.
  The Endangered Species Act of 1973 (ESA or Act), 87 Stat. 884,16 U. S. C. § 1631 (1988 ed. and'Supp. V), contains a variety of protections designed to save from extinction species that the Secretary of the Interior designates as endangered or threatened. Section 9 of the Act makes it unlawful for any person to “take” any endangered or threatened species. The Secretary has promulgated a regulation that defines the statute’s prohibition on takings to include “significant habitat modification or degradation where it actually kills or injures wildlife.” This case presents the question whether the Secretary exceeded his authority under the Act by promulgating that regulation.
  I
  Section 9(a)(1) of the Act provides the following protection for endangered species:
  “Except as provided in sections 1535(g)(2) and 1539 of this title, with respect to any endangered species of fish or wildlife listed pursuant to section 1533 of this title it is unlawful for any person subject to the jurisdiction of the United States to—
  “(B) take any such species within the United States or the territorial sea of the United States.” 16 U. S. C. § 1538(a)(1).
  Section 3(19) of the Act defines the statutory term “take”:
  “The term ‘take’ means to harass, harm, pursue, hunt, shoot, wound, kill, trap, capture, or collect, or to attempt to engage in any such conduct.” 16 U. S. C. § 1532(19).
  The Act does not further define the terms it uses to define “take.” The Interior Department regulations that implement the statute, however, define the statutory term “harm”:
  “Harm, in the definition of ‘take’ in the Act means an act which actually kills or injures wildlife. Such act may include significant habitat modification or degradation where it actually kills or injures wildlife by significantly impairing essential behavioral patterns, including breeding, feeding, or sheltering.” 50 CFR § 17.3 (1994).
  This regulation has been in place since 1975.
  A limitation on the §9 “take” prohibition appears in § 10(a)(1)(B) of the Act, which Congress added by amendment in 1982. That section authorizes the Secretary to grant a permit for any taking otherwise prohibited by § 9(a)(1)(B) “if such taking is incidental to, and not the purpose of, the carrying out of an otherwise lawful activity.” 16 U. S. C. § 1539(a)(1)(B).
  In addition to the prohibition on takings, the Act provides several other protections for endangered species. Section 4, 16 U. S. C. § 1533, commands the Secretary to identify species of fish or wildlife that are in danger of extinction and to publish from time to time lists of all species he determines to be endangered or threatened. Section 5, 16 U. S. C. § 1534, authorizes the Secretary, in cooperation with the States, see § 1535, to acquire land to aid in preserving such species. Section 7 requires federal agencies to ensure that none of their activities, including the granting of licenses and permits, will jeopardize the continued existence of endangered species “or result in the destruction or adverse modification of habitat of such species which is determined by the Secretary ... to be critical.” 16 U. S. C. § 1536(a)(2).
  Respondents in this action are small landowners, logging companies, and families dependent on the forest products industries in the Pacific Northwest and in the Southeast, and organizations that represent their interests. They brought this declaratory judgment action against petitioners, the Secretary of the Interior and the Director of the Fish and Wildlife Service, in the United States District Court for the District of Columbia to challenge the statutory validity of the Secretary’s regulation defining “harm,” particularly the inclusion of habitat modification and degradation in the definition. Respondents challenged the regulation on its face. Their complaint alleged that application of the “harm” regulation to the red-cockaded woodpecker, an endangered species, and the northern spotted owl, a threatened species, had injured them economically. App. 17-23.
  Respondents advanced three arguments to support their submission that Congress did not intend the word “take” in § 9 to include habitat modification, as the Secretary’s “harm” regulation provides. First, they correctly noted that language in the Senate’s original version of the ESA would have defined “take” to include “destruction, modification, or curtailment of [the] habitat or range” of fish or wildlife, but the Senate deleted that language from the bill before enacting it. Second, respondents argued that Congress intended the Act’s express authorization for the Federal Government to buy private land in order to prevent habitat degradation in § 5 to be the exclusive check against habitat modification on private property. Third, because the Senate added the term “harm” to the definition of “take” in a floor amendment without debate, respondents argued that the court should not interpret the term so expansively as to include habitat modification.
  The District Court considered and rejected each of respondents’ arguments, finding “that Congress intended an expansive interpretation of the word ‘take,’ an interpretation that encompasses habitat modification.” 806 F. Supp. 279, 285 (1992). The court noted that in 1982, when Congress was aware of a judicial decision that had applied the Secretary’s regulation, see Palila v. Hawaii Dept. of Land and Natural Resources, 639 F. 2d 495 (CA9 1981) (Palila I), it amended the Act without using the opportunity to change the definition of “take.” 806 F. Supp., at 284. The court stated that, even had it found the ESA “‘silent or ambiguous’” as to the authority for the Secretary’s definition of “harm,” it would nevertheless have upheld the regulation as a reasonable interpretation of the statute. Id., at 285 (quoting Chevron U. S. A. Inc. v. Natural Resources Defense Council, Inc., 467 U. S. 837, 843 (1984)). The District Court therefore entered summary judgment for petitioners and dismissed respondents’ complaint.
  A divided panel of the Court of Appeals initially affirmed the judgment of the District Court. 1 F. 3d 1 (CADC 1993). After granting a petition for rehearing, however, the panel reversed. 17 F. 3d 1463 (CADC 1994). Although acknowledging that “[t]he potential breadth of the word ‘harm’ is indisputable,” id., at 1464, the majority concluded that the immediate statutory context in which “harm” appeared counseled against a broad reading; like the other words in the definition of “take,” the word “harm” should be read as applying only to “the perpetrator’s direct application of force against the animal taken .... The forbidden acts fit, in ordinary language, the basic model ‘A hit B.’ ” Id., at 1465. The majority based its reasoning on a canon of statutory construction called noscitur a sociis, which holds that a word is known by the company it keeps. See Neal v. Clark, 95 U. S. 704, 708-709 (1878).
  The majority claimed support for its construction from a decision of the Ninth Circuit that narrowly construed the word “harass” in the Marine Mammal Protection Act of 1972, 16 U. S. C. § 1372(a)(2)(A), see United States v. Hayashi, 5 F. 3d 1278, 1282 (1993); from the legislative history of the ESA; from its view that Congress must not have intended the purportedly broad curtailment of private property rights that the Secretary’s interpretation permitted; and from the ESA’s land acquisition provision in §5 and restriction on federal agencies’ activities regarding habitat in §7, both of which the court saw as evidence that Congress had not intended the §9 “take” prohibition to reach habitat modification. Most prominently, the court performed a lengthy analysis of the 1982 amendment to §10 that provided for “incidental take permits” and concluded that the amendment did not change the meaning of the term “take” as defined in the 1973 statute.
  Chief Judge Mikva, who had announced the panel's original decision, dissented. See 17 F. 3d, at 1473. In his view, a proper application of Chevron indicated that the Secretary had reasonably defined “harm,” because respondents had failed to show that Congress unambiguously manifested its intent to exclude habitat modification from the ambit of “take.” Chief Judge Mikva found the majority’s reliance on noscitur a sociis inappropriate in light of the statutory language and unnecessary in light of the strong support in the legislative history for the Secretary’s interpretation. He did not find the 1982 “incidental take permit” amendment alone sufficient to vindicate the Secretary’s definition of “harm,” but he believed the amendment provided additional support for that definition because it reflected Congress’ view in 1982 that the definition was reasonable.
  The Court of Appeals’ decision created a square conflict with a 1988 decision of the Ninth Circuit that had upheld the Secretary’s definition of “harm.” See Palila v. Hawaii Dept. of Land and Natural Resources, 852 F. 2d 1106 (1988) (Palila II). The Court of Appeals neither cited nor distinguished Palila II, despite the stark contrast between the Ninth Circuit’s holding and its own. We granted certiorari to resolve the conflict. 513 U. S. 1072 (1995). Our consideration of the text and structure of the Act, its legislative history, and the significance of the 1982 amendment persuades us that the Court of Appeals’ judgment should be reversed.
  II
  Because this case was decided on motions for summary-judgment, we may appropriately make certain factual assumptions in order to frame the legal issue. First, we assume respondents have no desire to harm either the red-cockaded woodpecker or the spotted owl; they merely wish to continue logging activities that would be entirely proper if not prohibited by the ESA. On the other hand, we must assume, arguendo, that those activities will have the effect, even though unintended, of detrimentally changing the natural habitat of both listed species and that, as a consequence, members of those species will be killed or injured. Under respondents’ view of the law, the Secretary’s only means of forestalling that grave result — even when the actor knows it is certain to occur — is to use his §5 authority to purchase the lands on which the survival of the species depends. The Secretary, on the other hand, submits that the § 9 prohibition on takings, which Congress defined to include “harm,” places on respondents a duty to avoid harm that habitat alteration will cause the birds unless respondents first obtain a permit pursuant to § 10.
  The text of the Act provides three reasons for concluding that the Secretary’s interpretation is reasonable. First, an ordinary understanding of the word “harm” supports it. The dictionary definition of the verb form of “harm” is “to cause hurt or damage to: injure.” Webster’s Third New International Dictionary 1034 (1966). In the context of the ESA, that definition naturally encompasses habitat modification that results in actual injury or death to members of an endangered or threatened species.
  Respondents argue that the Secretary should have limited the purview of “harm” to direct applications of force against protected species, but the dictionary definition does not include the word “directly” or suggest in any way that only direct or willful action that leads to injury constitutes “harm.” Moreover, unless the statutory term “harm” encompasses indirect as well as direct injuries, the word has no meaning that does not duplicate the meaning of other words that §3 uses to define “take.” A reluctance to treat statutory terms as surplusage supports the reasonableness of the Secretary’s interpretation. See, e. g., Mackey v. Lanier Collection Agency & Service, Inc., 486 U. S. 825, 837, and n. 11 (1988).
  Second, the broad purpose of the ESA supports the Secretary’s decision to extend protection against activities that cause the precise harms Congress enacted the statute to avoid. In TVA v. Hill, 437 U. S. 153 (1978), we described the Act as “the most comprehensive legislation for the preservation of endangered species ever enacted by any nation.” Id., at 180. Whereas predecessor statutes enacted in 1966 and 1969 had not contained any sweeping prohibition against the taking of endangered species except on federal lands, see id., at 175, the 1973 Act applied to all land in the United States and to the Nation’s territorial seas. As stated in § 2 of the Act, among its central purposes is “to provide a means whereby the ecosystems upon which endangered species and threatened species depend may be conserved . . . .” 16 U. S. C. § 1531(b).
  In Hill, we construed § 7 as precluding the completion of the Tellico Dam because of its predicted impact on the survival of the snail darter. See 437 U. S., at 193. Both our holding and the language in our opinion stressed the importance of the statutory policy. “The plain intent of Congress in enacting this statute,” we recognized, “was to halt and reverse the trend toward species extinction, whatever the cost. This is reflected not only in the stated policies of the Act, but in literally every section of the statute.” Id., at 184. Although the §9 “take” prohibition was not at issue in Hill, we took note of that prohibition, placing particular emphasis on the Secretary’s inclusion of habitat modification in his definition of “harm.” In light of that provision for habitat protection, we could “not understand how TVA intends to operate Tellico Dam without ‘harming’ the snail darter.” Id., at 184, n. 30. Congress’ intent to provide comprehensive protection for endangered and threatened species supports the permissibility of the Secretary’s “harm” regulation.
  Respondents advance strong arguments that activities that cause minimal or unforeseeable harm will not violate the Act as construed in the “harm” regulation. Respondents, however, present a facial challenge to the regulation. Cf. Anderson v. Edwards, 514 U. S. 143, 155-156, n. 6 (1995); INS v. National Center for Immigrants’ Rights, Inc., 502 U. S. 183, 188 (1991). Thus, they ask us to invalidate the Secretary’s understanding of “harm” in every circumstance, even when an actor knows that an activity, such as draining a pond, would actually result in the extinction of a listed species by destroying its habitat. Given Congress’ clear expression of the ESA’s broad purpose to protect endangered and threatened wildlife, the Secretary’s definition of “harm” is reasonable.
  Third, the fact that Congress in 1982 authorized the Secretary to issue permits for takings that § 9(a)(1)(B) would otherwise prohibit, “if such taking is incidental to, and not the purpose of, the carrying out of an otherwise lawful activity,” 16 U. S. C. § 1539(a)(1)(B), strongly suggests that Congress understood § 9(a)(1)(B) to prohibit indirect as well as deliberate takings. Cf. NLRB v. Bell Aerospace Co., 416 U. S. 267, 274-275 (1974). The permit process requires the applicant to prepare a “conservation plan” that specifies how he intends to “minimize and mitigate” the “impact” of his activity on endangered and threatened species, 16 U. S. C. § 1539(a)(2)(A), making clear that Congress had in mind foreseeable rather than merely accidental effects on listed species. No one could seriously request an “incidental” take permit to avert §9 liability for direct, deliberate action against a member of an endangered' or threatened species, but respondents would read “harm” so narrowly that the permit procedure would have little more than that absurd purpose. “When Congress acts to amend a statute, we presume it intends its amendment to have real and substantial effect.” Stone v. INS, 514 U. S. 386, 397 (1995). Congress’ addition of the § 10 permit provision supports the Secretary’s conclusion that activities not intended to harm an endangered species, such as habitat modification, may constitute unlawful takings under the ESA unless the Secretary permits them.
  The Court of Appeals made three errors in asserting that “harm” must refer to a direct application of force because the words around it do. First, the court’s premise was flawed. Several of the words that accompany “harm” in the § 3 definition of “take,” especially “harass,” “pursue,” “wound,” and “kill,” refer to actions or effects that do not require direct applications of force. Second, to the extent the court read a requirement of intent or purpose into the words used to define “take,” it ignored § ll’s express provision that a “know-in[g]” action is enough to violate the Act. Third, the court employed noscitur a sociis to give “harm” essentially the same function as other words in the definition, thereby denying it independent meaning. The canon, to the contrary, counsels that a word “gathers meaning from the words around it.” Jarecki v. G. D. Searle & Co., 367 U. S. 303, 307 (1961). The statutory context of “harm” suggests that Congress meant that term to serve a particular function in the ESA, consistent with, but distinct from, the functions of the other verbs used to define “take.” The Secretary’s interpretation of “harm” to include indirectly injuring endangered animals through habitat modification permissibly interprets “harm” to have “a character of its own not to be submerged by its association.” Russell Motor Car Co. v. United States, 261 U. S. 514, 519 (1923).
  Nor does the Act’s inclusion of the § 5 land acquisition authority and the § 7 directive to federal agencies to avoid destruction or adverse modification of critical habitat alter our conclusion. Respondents’ argument that the Government lacks any incentive to purchase land under §5 when it can simply prohibit takings under § 9 ignores the practical considerations that attend enforcement of the ESA. Purchasing habitat lands may well cost the Government less in many circumstances than pursuing civil or criminal penalties. In addition, the § 5 procedure allows for protection of habitat before the seller’s activity has harmed any endangered animal, whereas the Government cannot enforce the § 9 prohibition until an animal has actually been killed or injured. The Secretary may also find the § 5 authority useful for preventing'modification of land that is not yet but may in the future become habitat for an endangered or threatened species. The §7 directive applies only to the Federal Government, whereas the § 9 prohibition applies to “any person.” Section 7 imposes a broad, affirmative duty to avoid adverse habitat modifications that §9 does not replicate, and §7 does not limit its admonition to habitat modification that “actually kills or injures wildlife.” Conversely, §7 contains limitations that §9 does not, applying only to actions “likely to jeopardize the continued existence of any endangered species or threatened species,” 16 U. S. C. § 1536(a)(2), and to modifications of habitat that has been designated “critical” pursuant to § 4, 16 U. S. C. § 1533(b)(2). Any overlap that § 5 or §7 may have with §9 in particular cases is unexceptional, see, e. g., Russello v. United States, 464 U. S. 16, 24, and n. 2 (1983), and simply reflects the broad purpose of the Act set out in § 2 and acknowledged in TVA v. Hill.
  We need not decide whether the statutory definition of “take” compels the Secretary’s interpretation of “harm,” because our conclusions that Congress did not unambiguously manifest its intent to adopt respondents’ view and that the Secretary’s interpretation is reasonable suffice to decide this case. See generally Chevron U. S. A. Inc. v. Natural Resources Defense Council, Inc., 467 U. S. 837 (1984). The latitude the ESA gives the Secretary in enforcing the statute, together with the degree of regulatory expertise necessary to its enforcement, establishes that we owe some degree of deference to the Secretary’s reasonable interpretation. See Breyer, Judicial Review of Questions of Law and Policy, 38 Admin. L. Rev. 363, 373 (1986).
  H-t H — t
  Our conclusion that the Secretary’s definition of “harm rests on a permissible construction of the ESA gains further support from the legislative history of the statute. The Committee Reports accompanying the bills that became the ESA do not specifically discuss the meaning of “harm,” but they make clear that Congress intended “take” to apply broadly to cover indirect as well as purposeful actions. The Senate Report stressed that “‘[t]ake’ is defined ... in the broadest possible manner to include every conceivable way in which a person can ‘take’ or attempt to ‘take’ any fish or wildlife.” S. Rep. No. 93-307, p. 7 (1973). The House Report stated that “the broadest possible terms” were used to define restrictions on takings. H. R. Rep. No. 93-412, p. 15 (1973). The House Report underscored the breadth of the “take” definition by noting that it included “harassment, whether intentional or not.” Id., at 11 (emphasis added). The Report explained that the definition “would allow, for example, the Secretary to regulate or prohibit the activities of birdwatchers where the effect of those activities might disturb the birds and make it difficult for them to hatch or raise their young.” Ibid. These comments, ignored in the dissent’s welcome but selective foray into legislative history, see post, at 726-729, support the Secretary’s interpretation that the term “take” in § 9 reached far more than the deliberate actions of hunters and trappers.
  Two endangered species bills, S. 1592 and S. 1983, were introduced in the Senate and referred to the Commerce Committee. Neither bill included the word “harm” in its definition of “take,” although the definitions otherwise closely resembled the one that appeared in the bill as ultimately enacted. See Hearings on S. 1592 and S. 1983 before the Subcommittee on Environment of the Senate Committee on Commerce, 93d Cong., 1st Sess., pp. 7, 27 (1973) (hereinafter Hearings). Senator Tunney, the floor manager of the bill in the Senate, subsequently introduced a floor amendment that added “harm” to the definition, noting that this and accompanying amendments would “help to achieve the purposes of the bill.” 119 Cong. Rec. 25683 (1973). Respondents argue that the lack of debate about the amendment that added “harm” counsels in favor of a narrow interpretation. We disagree. An obviously broad word that the Senate went out of its way to add to an important statutory definition is precisely the sort of provision that deserves a respectful reading.
  The definition of “take” that originally appeared in S. 1983 differed from the definition as ultimately enacted in one other significant respect: It included “the destruction, modification, or curtailment of [the] habitat or range” of fish and wildlife. Hearings, at 27. Respondents make much of the fact that the Commerce Committee removed this phrase from the “take” definition before S. 1983 went to the floor. See 119 Cong. Rec. 25663 (1973). We do not find that fact especially significant. The legislative materials contain no indication, why the habitat protection provision was deleted. That provision differed greatly from the regulation at issue today. Most notably, the habitat protection provision in S. 1983 would have applied far more broadly than the regulation does because it made adverse habitat modification a categorical violation of the “take” prohibition, unbounded by the regulation’s limitation to habitat modifications that actually kill or injure wildlife. The S. 1983 language also failed to qualify “modification” with the regulation’s limiting adjective “significant.” We do not believe the Senate’s unelabo-rated disavowal of the provision in S. 1983 undermines the reasonableness of the more moderate habitat protection in the Secretary’s “harm” regulation.
  The history of the 1982 amendment that gave the Secretary authority to grant permits for “incidental” takings provides further support for his reading of the Act. The House Report expressly states that “[b]y use of the word ‘incidental’ the Committee intends to cover situations in which it is known that a taking will occur if the other activity is engaged in but such taking is incidental to, and not the purpose of, the activity.” H. R. Rep. No. 97-567, p. 31 (1982). This reference to the foreseeability of incidental takings undermines respondents’ argument that the 1982 amendment covered only accidental killings of endangered and threatened animals that might occur in the course of hunting or trapping other animals. Indeed, Congress had habitat modification directly in mind: Both the Senate Report and the House Conference Report identified as the model for the permit process a cooperative state-federal response to a case in California where a development project threatened incidental harm to a species of endangered butterfly by modification of its habitat. See S. Rep. No. 97-418, p. 10 (1982); H. R. Conf. Rep. No. 97-835, pp. 30-32 (1982). Thus, Congress in 1982 focused squarely on the aspect of the “harm” regulation at issue in this litigation. Congress’ implementation of a permit program is consistent with the Secretary’s interpretation of the term “harm.”
  IV
  When it enacted the ESA, Congress delegated broad administrative and interpretive power to the Secretary. See 16 U. S. C. §§ 1533, 1540(f). The task of defining and listing endangered and threatened species requires an expertise and attention to detail that exceeds the normal province of Congress. Fashioning appropriate standards for issuing permits under § 10 for takings that would otherwise violate § 9 necessarily requires the exercise of broad discretion. The proper interpretation of a term such as “harm” involves a complex policy choice. When Congress has entrusted the Secretary with broad discretion, we are especially reluctant to substitute our views of wise policy for his. See Chevron, 467 U. S., at 865-866. In this case, that reluctance accords with our conclusion, based on the text, structure, and legislative history of the ESA, that the Secretary reasonably construed the intent of Congress when he defined “harm” to include “significant habitat modification or degradation that actually kills or injures wildlife.”
  In the elaboration and enforcement of the ESA, the Secretary and all persons who must comply with the law will confront difficult questions of proximity and degree; for, as all recognize, the Act encompasses a vast range of economic and social enterprises and endeavors. These questions must be addressed in the usual course of the law, through case-by-case resolution and adjudication.
  The judgment of the Court of Appeals is reversed.
  It is so ordered.
  The Act defines the term “endangered species” to mean “any species which is in danger of extinction throughout all or a significant portion of its range other than a species of the Class Insecta determined by the Secretary to constitute a pest whose protection under the provisions of this chapter would present an overwhelming and overriding risk to man.” 16 U.S. C. §1532(6).
  The Secretary, through the Director of the Fish and Wildlife Service, originally promulgated the regulation in 1975 and amended it in 1981 to emphasize that actual death or injury of a protected animal is necessary for a violation. See 40 Fed. Reg. 44412,44416 (1975); 46 Fed. Reg. 54748, 54750 (1981).
  Respondents also argued in the District Court that the Secretary’s definition of “harm” is unconstitutionally void for vagueness, but they do not press that argument here.
  The woodpecker was listed as an endangered species in 1970 pursuant to the statutory predecessor of the ESA. See 50 CFR § 17.11(h) (1994), issued pursuant to the Endangered Species Conservation Act of 1969, 83 Stat. 275.
  See 55 Fed. Reg. 26114 (1990). Another regulation promulgated by the Secretary extends to threatened species, defined in the ESA as “any .species which is likely to become an endangered species within the foreseeable future throughout all or a significant portion of its range,” 16 U. S. C. § 1532(20), some but not all of the protections endangered species enjoy. See 50 CFR § 17.31(a) (1994). In the District Court respondents unsuccessfully challenged that regulation’s extension of § 9 to threatened species, but they do not press the challenge here.
  Senate 1983, reprinted in Hearings on S. 1592 and S. 1983 before the Subcommittee on Environment of the Senate Committee on Commerce, 93d Cong., 1st Sess., 27 (1973).
  Judge Sentelle filed a partial concurrence in which he declined to join the portions of the court’s opinion that relied on legislative history. See 17 F. 3d 1463, 1472 (CADC 1994).
  The 1982 amendment had formed the basis on which the author of the majority’s opinion on rehearing originally voted to affirm the judgment of the District Court. Compare 1 F. 3d 1, 11 (CADC 1993) (Williams, J., concurring in part), with 17 F. 3d, at 1467-1472.
  As discussed above, the Secretary’s definition of “harm” is limited to “act[s] which actually kil[l] or injurie] wildlife.” 50 CFR §17.3 (1994). In addition, in order to be subject to the Act’s criminal penalties or the more severe of its civil penalties, one must “knowingly violatfe]” the Act or its implementing regulations. 16 U. S. C. §§ 1540(a)(1), (b)(1). Congress added “knowingly” in place of “willfully” in 1978 to make “criminal violations of the act a general rather than a specific intent crime.” H. R. Conf. Rep. No. 95-1804, p. 26 (1978). The Act does authorize up to a $500 civil fine for “[a]ny person who otherwise violates” the Act or its implementing regulations. 16 U. S. C. § 1540(a)(1). That provision is potentially sweeping, but it would be so with or without the Secretary’s “harm” regulation, making it unhelpful in assessing the reasonableness of the regulation. We have imputed scienter requirements to criminal statutes that impose sanctions without expressly requiring scienter, see, e. g., Staples v. United States, 511 U. S. 600 (1994), but the proper case in which we might consider whether to do so in the § 9 provision for a $500 civil penalty would be a challenge to enforcement of that provision itself, not a challenge to a regulation that merely defines a statutory term. We do not agree with the dissent that the regulation covers results that are not “even foreseeable ... no matter how long the chain of causality between modification and injury.” Post, at 715. Respondents have suggested no reason why either the “knowingly violates” or the “otherwise violates” provision of the statute — or the “harm” regulation itself — should not be read to incorporate ordinary requirements of proximate causation and foreseeability. In any event, neither respondents nor their amici have suggested that the Secretary employs the “otherwise violates” provision with any frequency.
  Respondents and the dissent emphasize what they portray as the “established meaning” of “take” in the sense of a “wildlife take,” a meaning respondents argue extends only to “the effort to exercise dominion over some creature, and the concrete effect of [sic] that creature.” Brief for Respondents 19; see post, at 717-718. This limitation ill serves the statutory text, which forbids not taking “some creature” but “tak[ing] any [endangered] species" — a formidable task for even the most rapacious feudal lord. More importantly, Congress explicitly defined the operative term “take” in the ESA, no matter how much the dissent wishes otherwise, see post, at 717-720, 722-723, thereby obviating the need for us to probe its meaning as we must probe the meaning of the undefined subsidiary term “harm.” Finally, Congress’ definition of “take” includes several words— most obviously “harass,” “pursue,” and “wound,” in addition to “harm” itself — that fit respondents’ and the dissent’s definition of “take” no better than does “significant habitat modification or degradation.”
  In contrast, if the statutory term “harm” encompasses such indirect means of killing and injuring wildlife as habitat modification, the other terms listed in §3 — “harass,” “pursue,” “hunt,” “shoot,” “wound,” “kill,” “trap,” “capture,” and “collect” — generally retain independent meanings. Most of those terms refer to deliberate actions more frequently than does “harm,” and they therefore do not duplicate the sense of indirect causation that “harm” adds to the statute. In addition, most of the other words in the definition describe either actions from which habitat modification does not usually result (e. g., “pursue,” “harass”) or effects to which activities that modify habitat do not usually lead (e. g., “trap,” “collect”). To the extent the Secretary’s definition of “harm” may have applications .that overlap with other words in the definition, that overlap reflects the broad purpose of the Act. See infra this page and 699-700.
  We stated: “The Secretary of the Interior has defined the term ‘harm’ to mean ‘an act or omission which actually injures or kills wildlife, including acts which annoy it to such an extent as to significantly disrupt essential behavioral patterns, which include, but are not limited to, breeding, feeding or sheltering; significant environmental modification or degradation which has such effects is included within the meaning of “harm.”’” TVA v. Hill, 437 U. S., at 184-185, n. 30 (citations omitted; emphasis in original).
  The dissent incorrectly asserts that the Secretary’s regulation (1) “dispenses with the foreseeability of harm” and (2) “fail[s] to require injury to particular animals,” post, at 731. As to the first assertion, the regulation merely implements the statute, and it is therefore subject to the statute’s “knowingly violates” language, see 16 U. S. C. §§ 1540(a)(1), (b)(1), and ordinary requirements of proximate causation and foreseeability. See n. 9, supra. Nothing in the regulation purports to weaken those requirements. To the contrary, the word “actually” in the regulation should be construed to limit the liability about which the dissent appears most concerned, liability under the statute’s “otherwise violates” provision. See n. 9, supra; post, at 721-722, 732-733. The Secretary did not need to include “actually” to connote “but for” causation, which the other words in the definition obviously require. As to the dissent’s second assertion, every term in the regulation’s definition of “harm” is subservient to the phrase “an act which actually kills or injures wildlife.”
  The dissent acknowledges the legislative history’s clear indication that the drafters of the 1982 amendment had habitat modification in mind, see post; at 730, but argues that the text of the amendment requires a contrary conclusion. This argument overlooks the statute’s requirement of a “conservation plan,” which must describe an alternative to a known, but undesired, habitat modification.
  The dissent makes no effort to defend the Court of Appeals’ reading of the statutory definition as requiring a direct application of force. Instead, it tries to impose on § 9 a limitation of liability to “affirmative conduct intentionally directed against a particular animal or animals.” Post, at 720. Under the dissent’s interpretation of the Act, a developer could drain a pond, knowing that the act would extinguish an endangered species of turtles, without even proposing a conservation plan or applying for a permit under § 10(a)(1)(B); unless the developer was motivated by a desire “to get at a turtle,” post, at 721, no statutory taking could occur. Because such conduct would not constitute a taking at common law, the dissent would shield it from § 9 liability, even though the words “kill” and “harm” in the statutory definition could apply to such deliberate conduct. We cannot accept that limitation. In any event, our reasons for rejecting the Court of Appeals’ interpretation apply as well to the dissent’s novel construction.
  Respondents’ reliance on United States v. Hayashi, 22 F. 3d 859 (CA9 1993), is also misplaced. Hayashi construed the term “harass,” part of the definition of “take” in the Marine Mammal Protection Act of 1972, 16 U. S. C. § 1361 et seq., as requiring a “direct intrusion” on wildlife to support a criminal prosecution. 22 F. 3d, at 864. Hayashi dealt with a challenge to a single application of a statute whose “take” definition includes neither “harm” nor several of the other words that appear in the ESA definition. Moreover, Hayashi was decided by a panel of the Ninth Circuit, the same court that had previously upheld the regulation at issue here in Palila II, 852 F. 2d 1106 (1988). Neither the Hayashi majority nor the dissent saw any need to distinguish or even to cite Palila II.
  Congress recognized that §§7 and 9 are not coextensive as to federal agencies when, in the wake of our decision in Hill in 1978, it added § 7(b), 16 U. S. C. § 1536(0), to the Act. That section provides that any federal project subject to exemption from §7, 16 U. S. C. § 1536(h), will also be exempt from § 9.
  Respondents also argue that the rule of lenity should foreclose any deference to the Secretary’s interpretation of the ESA because the statute includes criminal penalties. The rule of lenity is premised on two ideas: First, “ ‘a fair warning should be given to the world in language that the common world will understand, of what the law intends to do if a certain line is passed’ second, “legislatures and not courts should define criminal activity.” United States v. Bass, 404 U. S. 336, 347-350 (1971) (quoting McBoyle v. United States, 283 U. S. 25, 27 (1931)). We have applied the rule of lenity in a case raising a narrow question concerning the application of a statute that contains criminal sanctions to a specific factual dispute — whether pistols with short barrels and attachable shoulder stocks are short-barreled rifles — where no regulation was present. See United States v. Thompson/Center Arms Co., 504 U. S. 505, 517-518, and n. 9 (1992). We have never suggested that the rule of lenity should provide the standard for reviewing facial challenges to administrative regulations whenever the governing statute authorizes criminal enforcement. Even if there exist regulations whose interpretations of statutory criminal penalties provide such inadequate notice of potential liability as to offend the rule of lenity, the “harm” regulation, which has existed for two decades and gives a fair warning of its consequences, cannot be one of them.
  Respondents place heavy reliance for their argument that Congress intended the §5 land acquisition provision and not §9 to be the ESA’s remedy for habitat modification on a floor statement by Senator Tunney:
  “Many species have been inadvertently exterminated by a negligent destruction of their habitat. Their habitats have been cut in size, polluted, or otherwise altered so that they are unsuitable environments for natural populations of fish and wildlife. Under this bill, we can take steps to make amends for our negligent encroachment. The Secretary would be empowered to use the land acquisition authority granted to him in certain existing legislation to acquire land for the use of the endangered species programs. . . . Through these land acquisition provisions, we will be able to conserve habitats necessary to protect fish and wildlife from further destruction.
  “Although most endangered species are threatened primarily by the destruction of their natural habitats, a significant portion of these animals are subject to predation by man for commercial, sport, consumption, or other purposes. The provisions in S. 1983 would prohibit the commerce in or the importation, exportation, or taking of endangered species . .. .” 119 Cong. Rec. 25669 (1973).
  Similarly, respondents emphasize a floor statement by Representative Sullivan, the House floor manager for the ESA:
  “For the most part, the principal threat to animals stems from destruction of their habitat. . . . H. R. 37 will meet this problem by providing funds for acquisition of critical habitat It will also enable the Department of Agriculture to cooperate with willing landowners who desire to assist in the protection of endangered species, but who are understandably unwilling to do so at excessive cost to themselves.
  “Another hazard to endangered species arises from those who would capture or kill them for pleasure or profit. There is no way that Congress can make it less pleasurable for a person to take an animal, but we can certainly make it less profitable for them to do so.” Id., at 30162.
  Each of these statements merely explained features of the bills that Congress eventually enacted in §5 of the ESA and went on to discuss elements enacted in § 9. Neither statement even suggested that § 5 would be the Act’s exclusive remedy for habitat modification by private landowners or that habitat modification by private landowners stood outside the ambit of § 9. Respondents’ suggestion that these statements identified § 5 as the ESA’s only response to habitat modification contradicts their emphasis elsewhere on the habitat protections in § 7. See supra, at 702-703.
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