opinion: Mr. Justice Harlan
  announced the judgment of the Court in an opinion joined by The Chief Justice, Mr. Justice Douglas, and Mr. Justice Marshall.
  The Government directly appeals the order of the United States District Court for the District of Utah dismissing, on the ground of former jeopardy, an information charging the defendant-appellee with willfully assisting in the preparation of fraudulent income tax returns, in violation of 26 U. S. C. § 7206 (2).
  Appellee was_ originally charged in February 1968 with 25 counts of violating §7206 (2). He was . brought to trial before Chief Judge Ritter on August 27, 1968. After the jury was chosen and sworn, 14 of the counts were dismissed on the Government’s motion. The trial then commenced, the Government calling as its first witness an Internal Revenue Service agent in order to put in evidence the remaining 11 allegedly fraudulent income tax returns the defendant was charged with helping to prepare. At the trial judge’s suggestion, these exhibits were stipulated to and introduced in evidence without objection. The Government’s five remaining witnesses were taxpayers whom the defendant allegedly had aided in preparation of these returns.
  After the first of these witnesses was called, but prior to the commencement of direct examination, defense counsel suggested that these witnesses be’warned of their constitutional rights. The trial court agreed, and proceeded, in careful detail, to spell out the witness’ right not to say anything that might be used in a subsequent criminal prosecution against him and his right, in the event of such a prosecution, to be represented by an attorney. The first witness expressed a willingness to testify and stated that he had been warned of his. constitutional rights when the Internal Revenue Service first contacted him. The trial judge indicated, however, that he did not believe the witness had been given any warning at the time he was first contacted by the IRS, and refused to permit him to testify until he had consulted an attorney.
  The trial judge then asked the prosecuting attorney if his remaining four witnesses were similarly situated. The prosecutor responded that they had been warned of their rights by the' IRS upon initial contact. The judge, expressing the view that any warnings that might have been given were probably inadequate, proceéded to discharge the jury; he then called all the taxpayers, into court, and informed them of their constitutional rights and of the considerable dangers of unwittingly making damáging admissions in these factual circumstances. Finally, he aborted the trial so the witnesses could consult with attorneys.
  The case was set for retrial before another jury, but on pretrial motion by the defendant, Judge Ritter dismissed the information on the ground of former jeopardy. The Government filed a direct appeal to this Court, and we. noted probable jurisdiction. 396 U. S. 810 (1969). The case was argued at the 1969 Term and thereafter set for reargument at the present Term. 397 U. S. 1060 (1970).
  I
  Appellee contends, at the threshold, that our decision in United States v. Sisson, 399 U. S. 267, 302-307 (1970), which followed our noting of probable jurisdiction in this case, forecloses appeal by the Government under the motion-in-bar provisions of 18 U. S. C. § 3731 prior to its recent amendment. The question was fully briefed and argued on reargument.
  The statute provided, in relevant part, for an appeal by the Government direct to the Supreme Court “[f]rom the decision or judgment sustaining a motion in bar, when the defendant has not been put in jeopardy.” Appellee concedes, as indeed he must under the prior rulings of this Court, that his plea of former jeopardy constituted a “motion in bar” within the meaning of the statute. The issue is whether appellee had been “put in jeopardy” by virtue of the impaneling of the jury in the first proceeding before the declaration of mistrial. In Sisson, supra, the opinion of the Court— in discussing the applicability of the motion-in-bar provision to the Government's direct appeal of the trial judge's actions there — concluded, inter alia, that the “put in jeopardy” language applied whenever the jury had been impaneled, even if the defendant might constitutionally have been retried under the double jeopardy provisions of the Fifth Amendment. 399 U. S., at 302-307.
  Here the jury in the first proceeding had been impaneled before the mistrial ruling, but appellee’s motion to dismiss on grounds of former jeopardy was made prior to the impaneling of the second jury. The Government contends that the impaneling of the jury must be understood to apply to the jury in the proceeding to which the plea of former jeopardy is offered as a bar, rather than the jury whose impaneling was, in the first instance, essential to sustain the plea on the merits. Ap-pellee contends that the construction put on the statute ' in the Sisson opinion requires the conclusion that the Government may not appeal when a jury in the prior proceeding for the offense in question has been impaneled.
  We think the Government has the better of the argument. The Court’s opinion in Sisson dealt with the problem presented by the trial judge’s order puf porting to arrest the entry of judgment on the guilty verdict returned by the very jury whose impaneling was claimed to constitute “jeopardy” within the meaning of the motion-in-bar provision. The conclusion that jeopardy had attached by the impaneling of the jury in that proceeding rested on the view that the Congress was concerned, in granting the Government appeal rights in certain classes of eases, to avoid subjecting the defendant to a second trial where the first trial had terminated in á manner favorable to the defendant either because of a jury verdict or because of judicial action. . See Sisson, supra, at 293-300. The “compromise origins” of the Criminal Appeals Act, see id., at 307,. reflected this concern, and that concern is an important consideration supporting the canon of strict construction traditionally applied to this statute. See id., at 296-300; Will v. United States, 389 U. S. 90, 96-98 (1967).
  In the mistrial situation, the judicial ruling that is chronologically analogous to the Sisson, facts would be the declaration of a mistrial after the first jury has been impaneled. Obviously, the Government could not have appealed Judge Ritter’s. original declaration of mistrial. Since a mistrial ruling explicitly contemplates reprosecution of the defendant, the nonappealability of this judicial action fits with congressional action in excluding pleas in abatement from the class of cases warranting appellate review. The nonappealable status of rulings of this sort is fully explainable in terms of a policy disfavoring appeals from interlocutory rulings. See the discussion in Will v. United States, supra, at 96-98.
  But it does not follow from the nonappealability of rulings' which are essentially interlocutory insofar as they expressly contémplate resumption of the prosecution, that Congress intended to foreclose governmental appeal from the sustaining of a later motion in bar on the trial judge’s conclusion that constitutional double jeopardy policies require that the earlier mistrial ruling now be accorded the effect of barring reprosecution.' Indeed, when we recall that pleas of former jeopardy tyere the paradigm illustrations of motions in bar at common law, see n. 2, supra, it seems much more, likely that the congressional decision to allow governmental appeals from the judge’s decision sustaining a motion in bar was intended to permit review of later judicial, action possibly premised on erroneous theories concerning constitutional effects attaching to the earlier interlocutory ruling.
  Consistently with the Court’s opinion in Sisson, the sustaining of a motion in bar based on a plea of former jeopardy would be appealable as long as the motion in bar was sustained prior to the impaneling of the jury in the subsequent proceeding. Since Judge Ritter in this case dismissed the information on appellee’s plea of former jeopardy prior , to the impaneling of the second jury, .we conclude that the decision is directly appealable by the Government as a motion in bar before the defendant was “put in jeopardy” within the meaning of the applicable statute. Hence we proceed to the merits of appellee’s claim that reprosecution after the declaration of mistrial in the earlier proceeding would violate his Fifth Amendment rights.
  II
  The Fifth Amendment’s prohibition against placing a defendant “twice in jeopardy” represents a constitutional policy of finality for the defendant’s benefit.in federal criminal proceedings. ' A power’ in government to subject the individual to repeated prosecutions for the same offense would cut deeply into the framework of procedural protections which the Constitution establishes for the conduct of a criminal trial. And society’s awareness of the heavy personal strain which a criminal trial represents for the individual defendant is manifested in the willingness, to limit the Government to a single criminal proceeding to vindicate its very vital interest in enforcement of criminal laws. Both of these considerations are expressed in Green v. United States, 355 U. S. 184, 187-188 (1957), where the Court noted that the policy underlying this provision “is that the State with all its resources and power should not be allowed to make repeated attempts to convict an individual for an alleged offense, thereby subjecting him to embarrassment, expense and ordeal and compelling him to live in a continuing state of anxiety and insecurity,, as well as enhancing the possibility that even though innocent he may be found guilty.” These considerations have led this Court to conclude that a defendant is placed in jeopardy in a criminal proceeding once the defendant is put to trial before the trier of the facts, whether the • trier be a jury or a judge. See Green v. United States, supra, at 188; Wade v. Hunter, 336 U. S. 684, 688 (1949).
  But it is also true that- a criminal trial is, even in . the best of circumstances, a complicated affair to manage: The proceedings are dependent in the first instance oh the most elementary sort of considerations, e. g., the health of the various witnesses, parties, attorneys, jurors, etc., all of whom must be prepared to arrive at the courthouse at set times. And when one adds the scheduling problems arising from case overloads, and the Sixth Amendment’s requirement that the single trial to which the double jeopardy provision restricts the Governmént be conducted speedily, it becomes readily apparent that a mechanical rule prohibiting retrial whenever circumstances compel the discharge of a jury without the defendant's consent would be too high a price to pay for the added assurance of personal security and freedom from governmental harassment which such a mechanical rule would provide. As the Court noted in Wade v. Hunter, supra, at 689, “a- defendant’s valued right to have his trial completed , by a particular tribunal must in some circumstances be subordinated to the public’s interest in fair trials designed to end in just judgments.”
  Thus the conclusion that “jeopardy attaches” when the trial commences expresses a judgment that the constitutional policies underpinning the Fifth Amendment’s guarantee are implicated at that point in the proceed-' ings. The question remains, however, in what circumstances retrial is to be precluded when the initial proceedings are aborted prior to verdict without the defendant’s consent.
  In dealing with that question^ this Court has,, for the most part, explicitly declined the invitation of litigants to formulate rules based on categories of circumstances which will , permit or preclude retrial. Thus, in United States v. Perez, 9 Wheat. 579 (1824), this Court held that a defendant in a capital case might be retried after the trial judge had, without the defendant’s consent, discharged a jury that reported itself unable to'agree. Mr. Justice Story’s opinion for the Court in Perez expressed the following thoughts on the problem of reprosecution after a mistrial had been declared without the consent of the defendant:
  “We think, that in all cases of this nature, the law has invested Courts of justice with the authority to discharge a jury from giving any verdict, whenever, in their opinion, taking all the circumstances into . consideration, there is a manifest necessity for the act, or the ends of public justice would otherwise be defeated. They are to exercise a sound discretion on the subject; and it is impossible to define all the circumstances, which would render it proper to interfere. To be sure, the power ought to be used with the greatest caution, under urgent circumstances, and for very plain and obvious causes; and, in capital cases especially, Courts should be extremely careful how they interfere with any of the chances of life, in favour of the prisoner. But, after all, they have the right to order the discharge f and the security which the public have for the faithful, sound, and conscientious exercise of this discretion, rests, in this, as in other cases, upon the responsibility of the Judges, under their oaths of office.”. Id., at 580.
  The Perez case has since been applied by this Court as a standard of appellate review for testing the trial judge’s exercise of his discretion in declaring a mistrial without the defendant’s consent. E. g., Simmons v. United States, 142 U. S. 148 (1891) (reprosecution not-barred where mistrial declared because letter published in newspaper rendered juror’s impartiality doubtful); Logan v. United States, 144 U. S. 263 (1892) (reprose-cution not barred where jury discharged after 40 hours of deliberation for inability to reach a verdict); Thompson v. United States, 155 U. S. 271 (1894) (reprosecution not barred where jury discharged because one juror had ■ served on grand jury indicting defendant); Wade v. Hunter, 336 U. S. 684 (1949) (retrial not barred where military .court-martial discharged due to- tactical necessity in the field).
  But a more recent ease — Gori v. United States, 367 U. S. 364 (1961) — while adhering in the main to the Perez theme of a “manifest necessity” standard of appellate review — does suggest the possibility of a variation on that theme according to a determination by the appellate court as to which party to the case was the beneficiary of the mistrial ruling. In Gori, the Court was called upon to review the action of. a trial judge in discharging the jury when it appeared to the judge that the prosecution’s questioning of a witness might lead to the introduction of evidence of prior crimes. We upheld reprosecutiop after the mistrial in an opinion which, while applying the principle of Perez, appears to tie the judgment that there was no abuse of discretion in these circumstances to the fact that the judge- was acting “in the sole interest of the defendant.” 367 U. S., at 369; see also the dissenting opinion of Mr. Justice Douglas, id., at 370.
  In the instant cáse, the Government, relying principally on Gori, contends that even if we conclude the trial judge here abused his discretion, reprosecution should be permitted because the judge’s ruling “benefited” the defendant and also clearly was not compelled by bad-faith prosecutorial conduct aimed at triggering a mistrial in order to get another day in court. If the judgment as to who was “benefited” by the mistrial ruling turns on the appellate court’s conclusion concerning which party the trial judge was, in point of personal motivation, trying to protect from prejudice,, it seems reasonably clear from the trial record here that the judge’s insistence on stopping the trial until the witnesses were properly warned was motivated by the desire, to protect the witnesses rather than the defendant. But the Government appears to view the question of “benefit” as turning on an appellate court’s post hoc assessment as to which party would in fact have been aided in the hypothetical event that the witnesses had been called to the stand after consulting with their own attorneys on the course of conduct that would best serve to insulate them personally from criminal and civil liability for the fraudu-. lent tax returns. That conception of benefit, however, involves. nothing more than an' exercise in pure speculation. In sum, we are unable to conclude on this record that this is a case of a mistrial made “in the sole interest of the defendant.” See Gori v. United States, supra.
  Further, we think that a limitation on the abuse-of-discretion principle based on an appellate court’s assessment of which side benefited from the mistrial ruling does not adequately satisfy the policies underpinning the double jeopardy provision. Reprosecution after a mistrial has unnecessarily been declared by the trial court obviously subjects the defendant to the same personal strain and insecurity regardless of the motivation underlying the trial judge’s action. The Government contends, however, that the policies evinced by the double jeopardy provision do not reach this sort of injury; rather the unnecessarily inflicted second trial must, in the Government’s view, appear to be the result of a mistrial declaration which “unfairly aids the prosecution or harasses the defense.” Govt. Brief- 8.
  Certainly it is clear beyond question that the Double Jeopardy Clause does not guarantee a defendant that the Government will be prepared, in' all circumstances, to vindicate the social interest in law enforcement through the vehicle of a single proceeding for a .given offense. Thus, for. example, reprosecution for the same offense is permitted where the defendant wins a reversal on appeal of a conviction. United States v. Ball, 163 U. S. 662 (1896); see Green v. United States, 355 U. S. 184, 189 (1957). The determination to allow reprosecution in these circumstances reflects the judgment that the defendant's double jeopardy interests, however defined, do not go so- far as to compel society to so mobilize its decisionihaking resources that it will be prepared to assure the defendant a single proceeding free from harmful governmental or judicial error. But it is also clear that recognition that the defendant can be reprosecuted for the same offense after successful appeal does not compel the conclusion that double jeopardy policies are confined to prevention of prosecutorial or judicial overreaching. For the crucial difference between reprosecution after appeal by the. defendant and reprosecution, after a sua sponte judicial mistrial declaration is that in the first situation the defendant has not been deprived of his option to go to the first jury and, perhaps, end the, dispute then and. there with an acquittal. On the’ other hand, where the judge, acting without the defendant’s consent, aborts the proceeding, the defendant has béen deprived of his “valued right to have his trial completed by a particular tribunal.” See Wade v. Hunter, 336 U. S., at 689.
  If that right to go to a particular tribunal is valued, it is because, independent of the threat of bad-faith conduct by judge or prosecutor, the defendant has a significant interest in the decision whether or not to take the case from the jury when circumstances occur which might be thought to warrant a declaration of mistrial. Thus, where circumstances develop not attributable to prosecutorial or judicial overreaching, a motion by the defendant for mistrial is ordinarily assumed to remove any barrier to reprosecution, even if the defendant’s motion is necessitated by prosecutorial or judicial error. In the absence of such a motion, the Perez doctrine of manifest necessity stands as a command to trial judges not to foreclose the defendant’s option until a scrupulous exercise of judicial discretion leads to the conclusion that the ends of public justice would not be served by a continuation of the proceedings. See United States v. Perez, 9 Wheat., at 580.
  The conscious refusal of this Court to channel the exercise of that discretion according to rules based on categories of circumstances, see Wade v. Hunter, 336 U. S., at 691, reflects the elusive nature of the problem presented by judicial action. foreclosing the defendant from going to his jury. But that discretion must still be exercised; ■ unquestionably an important factor to be considered is the need to hold litigants on both sides to standards of responsible professional conduct in the clash of an adversary criminal process. Yet we cannot evolve rules based on the source of the particular problem giving rise to a question whether a mistrial should or should not be declared, because, even in circumstances where the problem reflects error on the part of one counsel or the other, the trial judge must still take care to assure himself that the situation warrants action on his part foreclosing the defendant from a potentially favorable judgment by the tribunal.
  In sum, counsel for both sides perform in an imperfect world; in this area, bright-line rules based on either the source of the problem or the intended beneficiary of the ruling would only disserve the vital competing interests of the-' Government and the defendant. ■ The trial judge must recognise that lack of preparedness by the Government . to continue the trial directly implicates policies •underpinning both the double jeopardy provisión and the speedy trial guarantee. Cf. Downum v. United States, 372 U. S. 734 (1963). Alternatively, the judge must bear in mind the potential risks of abuse by the defendant of society’s unwillingness to unnecessarily subject him to repeated prosecutions. Yet, in the final analysis, the judge must always temper the decision whether or not to abort the trial by considering the importance to the defendant of being able, once and for all, to conclude his confrontation with society through the verdict of a tribunal he might believe to be favorably disposed to his fate.
  III
  Applying these considerations to the record in this case, we must conclude that the trial judge here abused his discretion in discharging the jury. Despite assurances by both the first witness and the prosecuting attorney that the five taxpayers involved in the litigation had all been warned of their constitutional rights, the judge refused to permit them to testify, first expressing his disbelief that they were warned at all, and then ex-’ pressing his views that any- warnings that might have been given would be inadequate. App. 41^42. In probing the assumed inadequacy of the warnings that might have been given, the prosecutor was asked if he really intended to try a case for willfully aiding in the preparation of fraudulent returns on. a theory that would not incriminate the taxpayers. When the prosecutor started to answer that he intended to do just that, the judge cut him off in midstream and immediately discharged the jury. App. 42-43. It is apparent from the record that no consideration was given to. the possibility of a trial continuance; indeed, the trial judge acted so abruptly in discharging the jury that, had the prosecutor been disposed to suggest a continuance, or the defendant to object to the discharge of the jury, there would have been no opportunity to do. so. When one examines the circumstances surrounding the discharge of this jury, it seems abundantly apparent that the trial judge made no effort to exercise a sound discretion to assure that, taking all the circumstances into account, there was a manifest necessity for the sua sponte declaration of this mistrial. United States v. Perez, 9 Wheat., at 580. Therefore, we must conclude that in the circumstances of this case, appellee’s reprosecution would violate the double jeopardy provision of the Fifth Amendment.
  Affirmed.
  These provisions of the Criminal Appeals Act have recently been amended. See n. 6, infra. However, the new amendment does not apply to cases begun in the District Court before the effective date of enactment. Ibid. Our jurisdiction over the present appeal is therefore controlled by the terms of the Criminal Appeals Act as codified at 18 U. S. C. § 3731.
  The common-law equivalent of the motion in bar was used to raise the defenses of prior acquittal, prior conviction, and pardon. See United States v. Murdock, 284 U. S. 141, 151 (1931). Whether the motion-in-bar provision is construed broadly to reach any plea having the effect of preventing further prosecutions, see United States v. Mersky, 361 U. S. 431, 441-443 (1960) (BreiínaN, J., concurring), or narrowly to reach only pleas in the nature of confession and avoidance, see id., at 455-458 (Stewart, J., dissenting), appellee’s plea of former jeopardy based on the prior declaration of mistrial would be included. Cf. United States v. Blue, 384 U. S. 251, 254 (1966). See generally United States v. Sisson, 399 U. S. 267, 300 n. 53 (1970).
  The portion of the Court’s opinion in Sisson under discussion here was joined in by only four members of the Court.
  Mr. ■ Justice White’s , dissenting opinion contended that the jeopardy language applies to preclude governmental appeal only where the defendant’s reprosecution would be barred by the Constitution.
  The Government relies in part on United States v. Toteo, 377 U. S. 463 (1964), and United States v. Oppenheimer, 242 U. S. 85 (1916), as sustaining jurisdiction under 18 U. S. C. §3731 to review the trial court’s action- in granting a pretrial motion to dismiss on double jeopardy grounds after the prior proceeding ended in a mistrial. In Tateo, however, jurisdiction was neither raised by the parties nor considered by the Court; therefore, it is of little significance on the jurisdiction point. In Oppenheimer, the motion in bar in the second proceeding rested on an earlier pretrial motion based on the statute of limitations; the theory of the second plea ivas res judieata.
  Appellee points out that Rule 12 (b)(1) of the Federal Rules of Criminal Procedure permits the defendant to raise the defense of former jeopardy on motion before or after the impaneling of the jury. See Notes of the Advisory Committee, 8 J. Moore, Federal Practice ¶ 12.01 [2] (2d ed. 1970). Thus, it is suggested that the defendant may deprive the Government of its appeal simply by delaying his motion to dismiss until the jury has been impaneled. This' problem, of course,1 is inherent in the structure of the Criminal Appeals Act prior' to amendment; for example, the defendant under Rule 12 (b) (1) may also delay his statute of limitations plea until after the impaneling of the jury, see ibid., thereby depriving the Government of its § 3731 appeal to this Court. Soon after the passage of the original Act, the Attorney General recognized the problem and proposed that the Act be amended to require'counsel for the defendant to raise and argue such questions before jeopardy attaches. See Sisson, supra, at 305-306. A recently enacted amendment to the Criminal Appeals Act undertakes to. deal with the problem by allowing the Government to appeal “to a court of appeals from a decision, judgment, or order of a district court dismissing an indictment or information as to any one or more counts, except that no appeal shall lie where the double jeopardy clause of the United States Constitution prohibits further prosecution.” Omnibus Crime-Control Act of 1970, § 14 (a) (1), 84 Stat. 1890 (January 2, 1971). However, the amendment is not applicable -to any criminal case begun in any district court before the effective date of the amendment. Id., § 14 (b)'. See also S. Rep. No. 91-1296, pp. 6-7-
  It is clear from the record in this case that Judge Ritter’s action cannot, as two members of the Court suggest, be classified as an “acquittal” for purposes of this Court’s jurisdiction over the appeal under 18 U. S. C. § 3731. First, Judge Ritter’s action at the original trial clearly contemplated reprosecution of the defendant after the witnesses had consulted with attorneys. See App. 46 and-Mr. Justice Stewart’s dissent, post, at 488-489, n. 1. Judge Ritter’s subsequent action dismissing the information was simply put on the ground of defendant’s plea of former jeopardy, without further explanation. App. 60. But the parties below put the question of former jeopardy to Judge Ritter exclusively in terms of the Court’s line of cases concerning reprosecutability after mistrial declarations without the defendant’s consent. See App. 55-59, which contain the entire post-mistrial proceedings before Judge Ritter.
  Of course, as we noted in Sisson, supra, at 290, the trial judge’s characterization of his own action 'cannot control the classification of the action for purposes of our appellate jurisdiction. But Sisson goes on to articulate the criterion of an “acquittal” for purposes of assessing our jurisdiction to review: the trial judge’s disposition is an “acquittal” if it is “a legal determination on the basis of facts adduced at the trial relating to the general issue of the case . . . .” Sisson, supra, at 290 n. 19. The record in this case is utterly devoid of any indication of reliance by Judge Ritter on facts relating to the general issue of the case, thereby surely distinguishing this case from Sisson, and, one would think, under the very reasoning of Sisson, compelling the conclusion that whatever else Judge Ritter may have done, he did not “acquit” the defendant in the relevant sense:
  Two Terms ago the double jeopardy provision of the Fifth Amendment was made directly applicable to the States. See Benton V. Maryland, 395 U. S. 784 (1969).
  See also Annotation,: Double Jeopardy — Mistrial, 6 L. Ed) 2d 1509; J. Sigler, Double Jeopardy 39-47 (1969).
  And see Annotation, supra, n. 9, at 1511; Sigler, supra, n. 9, at 44-45.
  We think, that nothing said in United States v. Tateo, 377 U. S. 463, 467 (1964), can properly be taken as indicating a contrary view. For there, even though defendant’s ■ guilty plea which aborted the trial was subsequently held to have been coerced by judicial action, the defendant nonetheless was hot foreclosed of his option to go to the jury if he chose to do so, and thereafter rely on post-eonviction proceedings to redress the wrong done to him by the judge. In other words, the question of “voluntariness” for purposes of assessing the validity of a plea of guilty — whether offered before or at trial— must be distinguished from the question of “voluntariness” for purposes of assessing reprosecutability under the Double Jeopardy Clause.
  Conversely, where a defendant’s mistrial motion "is necessitated by -judicial or prosecutorial impropriety designed to avoid an acquittal, reprosecution might well be barred. Cf. United States v. Tateo, supra, at 468 n. 3; n. 11, supra.