Mr. Justice Stewart
delivered the opinion of the Court.
The petitioners were convicted by a jury in the District Court for the Southern District of New York of conspiring to import and conceal heroin in violation of the federal narcotics laws.1 An important part of the Gov[245]*245ernment’s evidence consisted of tape recordings of conversations among several of the petitioners in a New York City hotel room. The tapes were made by federal officers in the adjoining room by means of an electronic recording device which did not physically intrude into the petitioners’ room.2 Because there was no “trespass” or “actual intrusion into a constitutionally protected [246]*246area,” the District Court and the Court of Appeals rejected the petitioners’ argument that this evidence was inadmissible because the eavesdropping had violated their rights under the Fourth Amendment. The convictions were affirmed,3 and we granted certiorari to consider the constitutional questions thus presented.4
Last Term in Katz v. United States, 389 U. S. 347, we held that the reach of the Fourth Amendment “cannot turn upon the presence or absence of a physical intrusion into any given enclosure.” Id., at 363. Noting that the “Fourth Amendment protects people, not places,” id., at 351, we overruled cases holding that a search and seizure of speech requires some trespass or actual penetration of a particular enclosure. We concluded that since every electronic eavesdropping upon private conversations is a search or seizure, it can comply with constitutional standards only when authorized by a neutral magistrate upon a showing of probable cause and under precise limitations and appropriate safeguards. The eavesdropping in this case was not carried out pursuant to such a warrant, and the convictions must therefore be reversed if Katz is to be applied to electronic surveillance conducted before the date of that decision. We have concluded, however, that to the extent Katz departed from previous holdings of this Court, it should be given wholly prospective application. Accordingly, and because we find no merit in any of the petitioners’ other challenges to their convictions, we affirm the judgment before us.5
[247]*247We are met at the outset with the petitioners’ contention that Katz does not actually present a choice between prospective or retroactive application of new constitutional doctrine. The Court in that decision, it is said, did not depart from any existing interpretation of the Constitution, but merely confirmed the previous demise of obsolete decisions enunciating the distinction between “trespassory” searches and those in which there was no physical penetration of the protected premises. Goldman v. United States, 316 U. S. 129; Olmstead v. United States, 277 U. S. 438.6 But this contention misconstrues our opinion in Katz. Our holding there that Goldman [248]*248and Olmstead “can no longer be regarded as controlling,” 389 U. S., at 353, recognized that those decisions had not been overruled until that day.7 True, the principles they expressed had been modified. The belief that an oral conversation could not be the object of a “search” or “seizure” had not survived.8 And in Silverman v. United States, 365 U. S. 505, we had cautioned that the scope of the Fourth Amendment could not be ascertained by resort to the “ancient niceties of tort or real property law.” 365 U. S., at 511. But the assumption persisted that electronic surveillance did not offend the Constitution unless there was an “actual intrusion into a constitutionally protected area.”9 While decisions before Katz may have reflected growing dissatisfaction with the traditional tests of the constitutional validity of electronic surveillance,10 the Court consistently reiterated those tests and declined invitations to abandon them.11 However clearly our holding in Katz may have been foreshadowed, it was a clear break with the past, and we are thus compelled to decide whether its application should be limited to the future.
Ever since Linkletter v. Walker, 381 U. S. 618, 629, established that “the Constitution neither prohibits nor requires retrospective effect” for decisions expounding [249]*249new constitutional rules affecting criminal trials, the Court has viewed the retroactivity or nonretroactivity of such decisions as a function of three considerations. As we most recently summarized them in Stovall v. Denno, 388 U. S. 293, 297,
“The criteria guiding resolution of the question implicate (a) the purpose to be served by the new standards, (b) the extent of the reliance by law enforcement authorities on the old standards, and (c) the effect on the administration of justice of a retroactive application of the new standards.” 12
Foremost among these factors is the purpose to be served by the new constitutional rule.13 This criterion strongly supports prospectivity for a decision amplifying the evidentiary exclusionary rule. Thus, it was principally the Court’s assessment of the purpose of Mapp v. Ohio, 367 U. S. 643, which led it in Linkletter to deny those finally convicted the benefit of Mapp’s extension of the exclusionary rule to the States:
“all of the cases . . . requiring the exclusion of illegal evidence have been based on the necessity for an effective deterrent to illegal police action. . . . We cannot say that this purpose would be advanced by making the rule retrospective. The misconduct of the police . . . has already occurred and will not be corrected by releasing the prisoners involved.” 381 U. S., at 636-637.14
[250]*250We further observed that, in contrast with decisions which had been accorded retroactive effect,15 “there is no likelihood of unreliability or coercion present in a search- and-seizure case”; the exclusionary rule is but a “procedural weapon that has no bearing on guilt,” and “the fairness of the trial is not under attack.” 381 U. S., at 638, 639. Following this reasoning of Linkletter, we recently held in Fuller v. Alaska, 393 U. S. 80, that the exclusionary rule of Lee v. Florida, 392 U. S. 378, should be accorded only prospective application. Analogizing Lee to Mapp, we concluded that evidence seized in violation of § 605 of the Federal Communications Act16 was “no less relevant and reliable than that seized in violation of the Fourth Amendment,” and that both decisions were merely “designed to enforce the federal law.” 393 U. S., at 81.
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Mr. Justice Stewart
delivered the opinion of the Court.
The petitioners were convicted by a jury in the District Court for the Southern District of New York of conspiring to import and conceal heroin in violation of the federal narcotics laws.1 An important part of the Gov[245]*245ernment’s evidence consisted of tape recordings of conversations among several of the petitioners in a New York City hotel room. The tapes were made by federal officers in the adjoining room by means of an electronic recording device which did not physically intrude into the petitioners’ room.2 Because there was no “trespass” or “actual intrusion into a constitutionally protected [246]*246area,” the District Court and the Court of Appeals rejected the petitioners’ argument that this evidence was inadmissible because the eavesdropping had violated their rights under the Fourth Amendment. The convictions were affirmed,3 and we granted certiorari to consider the constitutional questions thus presented.4
Last Term in Katz v. United States, 389 U. S. 347, we held that the reach of the Fourth Amendment “cannot turn upon the presence or absence of a physical intrusion into any given enclosure.” Id., at 363. Noting that the “Fourth Amendment protects people, not places,” id., at 351, we overruled cases holding that a search and seizure of speech requires some trespass or actual penetration of a particular enclosure. We concluded that since every electronic eavesdropping upon private conversations is a search or seizure, it can comply with constitutional standards only when authorized by a neutral magistrate upon a showing of probable cause and under precise limitations and appropriate safeguards. The eavesdropping in this case was not carried out pursuant to such a warrant, and the convictions must therefore be reversed if Katz is to be applied to electronic surveillance conducted before the date of that decision. We have concluded, however, that to the extent Katz departed from previous holdings of this Court, it should be given wholly prospective application. Accordingly, and because we find no merit in any of the petitioners’ other challenges to their convictions, we affirm the judgment before us.5
[247]*247We are met at the outset with the petitioners’ contention that Katz does not actually present a choice between prospective or retroactive application of new constitutional doctrine. The Court in that decision, it is said, did not depart from any existing interpretation of the Constitution, but merely confirmed the previous demise of obsolete decisions enunciating the distinction between “trespassory” searches and those in which there was no physical penetration of the protected premises. Goldman v. United States, 316 U. S. 129; Olmstead v. United States, 277 U. S. 438.6 But this contention misconstrues our opinion in Katz. Our holding there that Goldman [248]*248and Olmstead “can no longer be regarded as controlling,” 389 U. S., at 353, recognized that those decisions had not been overruled until that day.7 True, the principles they expressed had been modified. The belief that an oral conversation could not be the object of a “search” or “seizure” had not survived.8 And in Silverman v. United States, 365 U. S. 505, we had cautioned that the scope of the Fourth Amendment could not be ascertained by resort to the “ancient niceties of tort or real property law.” 365 U. S., at 511. But the assumption persisted that electronic surveillance did not offend the Constitution unless there was an “actual intrusion into a constitutionally protected area.”9 While decisions before Katz may have reflected growing dissatisfaction with the traditional tests of the constitutional validity of electronic surveillance,10 the Court consistently reiterated those tests and declined invitations to abandon them.11 However clearly our holding in Katz may have been foreshadowed, it was a clear break with the past, and we are thus compelled to decide whether its application should be limited to the future.
Ever since Linkletter v. Walker, 381 U. S. 618, 629, established that “the Constitution neither prohibits nor requires retrospective effect” for decisions expounding [249]*249new constitutional rules affecting criminal trials, the Court has viewed the retroactivity or nonretroactivity of such decisions as a function of three considerations. As we most recently summarized them in Stovall v. Denno, 388 U. S. 293, 297,
“The criteria guiding resolution of the question implicate (a) the purpose to be served by the new standards, (b) the extent of the reliance by law enforcement authorities on the old standards, and (c) the effect on the administration of justice of a retroactive application of the new standards.” 12
Foremost among these factors is the purpose to be served by the new constitutional rule.13 This criterion strongly supports prospectivity for a decision amplifying the evidentiary exclusionary rule. Thus, it was principally the Court’s assessment of the purpose of Mapp v. Ohio, 367 U. S. 643, which led it in Linkletter to deny those finally convicted the benefit of Mapp’s extension of the exclusionary rule to the States:
“all of the cases . . . requiring the exclusion of illegal evidence have been based on the necessity for an effective deterrent to illegal police action. . . . We cannot say that this purpose would be advanced by making the rule retrospective. The misconduct of the police . . . has already occurred and will not be corrected by releasing the prisoners involved.” 381 U. S., at 636-637.14
[250]*250We further observed that, in contrast with decisions which had been accorded retroactive effect,15 “there is no likelihood of unreliability or coercion present in a search- and-seizure case”; the exclusionary rule is but a “procedural weapon that has no bearing on guilt,” and “the fairness of the trial is not under attack.” 381 U. S., at 638, 639. Following this reasoning of Linkletter, we recently held in Fuller v. Alaska, 393 U. S. 80, that the exclusionary rule of Lee v. Florida, 392 U. S. 378, should be accorded only prospective application. Analogizing Lee to Mapp, we concluded that evidence seized in violation of § 605 of the Federal Communications Act16 was “no less relevant and reliable than that seized in violation of the Fourth Amendment,” and that both decisions were merely “designed to enforce the federal law.” 393 U. S., at 81.
The second and third factors — reliance of law enforcement officials, and the burden on the administration of justice that would flow from a retroactive application— also militate in favor of applying Katz prospectively. Katz for the first time explicitly overruled the “physical penetration” and “trespass”, tests enunciated in earlier decisions of this Court. Our periodic restatements of those tests confirmed the interpretation that police and courts alike had placed on the controlling precedents and [251]*251fully justified reliance on their continuing validity. Nor had other courts theretofore held that the prohibitions of the Fourth Amendment encompassed “non-trespassory” electronic surveillance. On the contrary, only a few months before the eavesdropping in this case, the Court of Appeals for the Second Circuit had upheld the introduction of electronic evidence obtained by the same narcotics agent with a virtually identical installation. United States v. Pardo-Bolland, 348 F. 2d 316, cert. denied, 382 U. S. 944.
Although there apparently have not been many federal convictions based on evidence gathered by warrantless electronic surveillance,17 we have no cause to doubt that the number of state convictions obtained in reliance on pre-Katz decisions is substantial.18 Moreover, the determination of whether a particular instance of eavesdropping led to the introduction of tainted evidence at trial would in most cases be a difficult and time-consuming task, which, particularly when attempted long after the event, would impose a weighty burden on any court. Cf. Alderman v. United States, ante, at 180-185. It is to be noted also that we have relied heavily on the factors of the extent of reliance and consequent burden on the administration of justice only when the purpose of the rule in question did not clearly favor either retroactivity or prospectivity.19 Because the deterrent purpose of Katz overwhelmingly supports nonretroactivity, we [252]*252would reach that result even if relatively few convictions would be set aside by its retroactive application.
The petitioners argue that even if Katz is not given fully retrospective effect, at least it should govern those cases which, like the petitioners’, were pending on direct review when Katz was decided. Petitioners point out that in Linkletter, the only other case involving the retroactivity of a Fourth Amendment decision, the Court held Mapp applicable to every case still pending on direct review on the date of that decision. A similar approach was adopted in Tehan v. Shott, 382 U. S. 406, with respect to the prospectivity of Griffin v. California, 380 U. S. 609. In Johnson v. New Jersey, 384 U. S. 719, however, we abandoned the approach taken in Linkletter and Tehan and concluded that “there are no jurisprudential or constitutional obstacles” to the adoption of a different cut-off point. Id,., at 733. We explained that [253]*253Here, on the other hand, as in Johnson, “the possibility of applying [Katz] only prospectively is yet an open issue.” Ibid.
[252]*252“[o]ur holdings in Linkletter and Tehan were necessarily limited to convictions which had become final by the time Mapp and Griffin were rendered. Decisions prior to Linkletter and Tehan had already established without discussion that Mapp and Griffin applied to cases still on direct appeal at the time they were announced.” Id., at 732.20
[253]*253All of the reasons for making Katz retroactive also undercut any distinction between final convictions and those still pending on review. Both the deterrent purpose of the exclusionary rule and the reliance of law enforcement officers focus upon the time of the search, not any subsequent point in the prosecution, as the relevant date. Exclusion of electronic eavesdropping evidence seized before Katz would increase the burden on the administration of justice, would overturn convictions based on fair reliance upon pre-Katz decisions, and would not serve to deter similar searches and seizures in the future.
Nor can it sensibly be maintained that the Court is foreclosed by Linkletter in this case, as it was not in Johnson, simply because Katz, like Mapp, was a Fourth Amendment decision.21 In neither Linkletter nor Johnson was it intimated that the cut-off points there adopted depended in any degree on the constitutional provision involved. There is, moreover, a significant distinction between the Mapp and Katz decisions. Mapp dealt solely with the applicability of the exclusionary rule to the States; “the situation before Mapp . . . [was that] the States at least knew that they were constitutionally forbidden from engaging in unreasonable searches and seizures under Wolf v. Colorado, 338 U. S. 25 (1949).” 22 Before Katz on the other hand, “non-trespassory” electronic surveillance was not thought to fall within the [254]*254reach of the Fourth Amendment.23 Therefore, this case lacks whatever impetus the knowingly unconstitutional conduct by the States may have provided in Linkletter to apply Mapp to all pending prosecutions.
In sum, we hold that Katz is to be applied only to cases in which the prosecution seeks to introduce the fruits of electronic surveillance conducted after December 18, 1967.24 Since the eavesdropping in this case occurred before that date and was consistent with pre-Katz decisions of this Court, the convictions must be
Affirmed.
Mr. Justice Black, while adhering to his dissent in Linkletter v. Walker, 381 U. S. 618, 640 (1965), concurs in the affirmance of the judgment of convictions in this case for the reasons stated in his dissenting opinion in Katz v. United States, 389 U. S. 347, 364 (1967).
Mr. Justice Marshall took no part in the consideration or decision of this case.