The Fourth Amendment protects people, not places, and its reach does not depend on physical penetration into a constitutionally protected area; electronic eavesdropping on conversations made from a public phone booth, where the user has a justifiable expectation of privacy, constitutes a "search and seizure" requiring a warrant based on probable cause.

The case arose from an FBI investigation into the petitioner's suspected involvement in transmitting gambling information via telephone between Los Angeles, Miami, and Boston, in violation of federal law.

• FBI agents suspected the petitioner, Charles Katz, of transmitting wagering information by telephone in violation of 18 U.S.C. § 1084.
• Agents attached an electronic listening and recording device to the outside of a public telephone booth that Katz frequently used.
• Using this device, the agents overheard and recorded only Katz's end of his telephone conversations made from the booth.
• No physical penetration of the telephone booth occurred during the surveillance.
• The recordings of Katz's conversations were introduced as evidence against him at his trial.
• Katz was convicted based, in part, on this electronically obtained evidence.
• The surveillance was conducted without a prior judicial warrant.
• The agents confined their surveillance to the brief periods Katz used the booth and only listened to his conversations.

• Petitioner argued that a public telephone booth is a constitutionally protected area.
• Petitioner contended that evidence obtained by attaching an electronic listening/recording device to the top of the booth violated the user's right to privacy.
• Petitioner argued that physical penetration of the constitutionally protected area is not necessary for a search and seizure to violate the Fourth Amendment.

• The Government argued that its agents' activities did not violate the Fourth Amendment because they involved no physical entrance into the area occupied by the petitioner.
• The Government stressed that the telephone booth was partly constructed of glass, making the petitioner visible.
• The Government contended that the surveillance technique did not require testing by Fourth Amendment standards as it involved no physical penetration.
• The Government argued that even if it were a search, the agents acted reasonably, based on probable cause and limited scope/duration, and their actions should be retroactively validated as they relied on prior case law (Olmstead, Goldman).
• The Government urged the creation of an exception to the warrant requirement for surveillance of a telephone booth based on probable cause.

• Does the electronic listening to and recording of a person's conversations in a public telephone booth, conducted without physical penetration of the booth, constitute a "search and seizure" under the Fourth Amendment?
• If such electronic surveillance constitutes a search and seizure, must it be conducted pursuant to a warrant to be constitutionally valid under the Fourth Amendment?

• The Supreme Court reversed the judgment of the Court of Appeals.
• The Court held that the Government's eavesdropping activities violated the privacy upon which the petitioner justifiably relied while using the telephone booth and thus constituted a "search and seizure" within the meaning of the Fourth Amendment.
• The Court ruled that the Fourth Amendment protects people, not simply "areas," and the absence of physical intrusion into the booth was not constitutionally significant, thereby rejecting the "trespass" doctrine of Olmstead and Goldman.
• The Court determined that a person using a public telephone booth seeks to exclude the "uninvited ear," not necessarily the "intruding eye," and is entitled to assume his words will not be broadcast.
• The Court concluded that warrantless searches are per se unreasonable under the Fourth Amendment, subject only to a few established exceptions, none of which applied to this case.
• Although the surveillance might have been constitutionally permissible if authorized in advance by a magistrate under narrowly defined procedures, it was conducted without such prior judicial sanction, rendering the search unreasonable.

• Fourth Amendment Search and Seizure: The Court expanded the understanding of "search and seizure" to include the recording of oral statements overheard without any technical trespass, focusing on privacy rather than property interests. It was applied here to classify the electronic eavesdropping as a search and seizure.
• Reasonable Expectation of Privacy: The Court established (explicitly articulated in Harlan's concurrence) that Fourth Amendment protection applies where a person has exhibited an actual (subjective) expectation of privacy that society is prepared to recognize as reasonable. Katz's act of shutting the booth door and paying the toll created such an expectation.
• "People, not Places": The Court emphasized that the primary object of Fourth Amendment protection is the individual's privacy, not merely specific locations. This principle was used to detach the Amendment's applicability from the outdated requirement of physical intrusion into a designated "area."
• Warrant Requirement: The Court reaffirmed the fundamental rule that searches conducted without prior approval by a judge or magistrate are presumptively unreasonable under the Fourth Amendment. This rule was applied to invalidate the warrantless electronic surveillance conducted by the FBI agents, despite their claims of probable cause and restraint.
• Overruling of Trespass Doctrine (Olmstead & Goldman): The Court explicitly stated that the "trespass" doctrine, which previously required physical penetration for a Fourth Amendment violation in eavesdropping cases as held in Olmstead v. United States and Goldman v. United States, is no longer controlling.

• "the Fourth Amendment protects people, not places."
• "What a person knowingly exposes to the public, even in his own home or office, is not a subject of Fourth Amendment protection. . . . But what he seeks to preserve as private, even in an area accessible to the public, may be constitutionally protected."
• "The Government's activities in electronically listening to and recording the petitioner's words violated the privacy upon which he justifiably relied while using the telephone booth and thus constituted a 'search and seizure' within the meaning of the Fourth Amendment."
• "[T]he reach of that Amendment cannot turn upon the presence or absence of a physical intrusion into any given enclosure."
• "[S]earches conducted outside the judicial process, without prior approval by judge or magistrate, are per se unreasonable under the Fourth Amendment—subject only to a few specifically established and well-delineated exceptions."
• "[T]he 'trespass' doctrine there enunciated [in Olmstead and Goldman] can no longer be regarded as controlling."

• Olmstead v. United States, 277 U.S. 438: Cited as establishing the overruled "trespass" doctrine, which held that electronic eavesdropping without physical intrusion was not a Fourth Amendment search.
• Goldman v. United States, 316 U.S. 129: Also cited as establishing the overruled "trespass" doctrine for electronic surveillance without physical penetration.
• Silverman v. United States, 365 U.S. 505: Cited to show the Court had already begun to move away from the strict trespass doctrine, holding the Fourth Amendment extends to recording oral statements overheard without "technical trespass under . . . local property law," especially where physical intrusion (however slight) occurred. Also cited in Harlan's concurrence regarding electronic penetration.
• Warden v. Hayden, 387 U.S. 294: Cited for the proposition that the premise that property interests control the right to search and seize has been discredited, supporting the shift to privacy interests. Also cited regarding the "hot pursuit" exception (not applicable here).
• Osborn v. United States, 385 U.S. 323: Cited as an example where the Court approved court-authorized electronic surveillance under specific, narrow circumstances with procedural safeguards similar to a warrant.
• Berger v. New York, 388 U.S. 41: Discussed in relation to Osborn, highlighting the need for particularity and safeguards in warrants authorizing electronic surveillance. Contrasted in Justice Black's dissent.
• Weeks v. United States, 232 U.S. 383: Cited as establishing that a private home is a constitutionally protected area (Harlan's concurrence) and as the origin of the exclusionary rule (Black's dissent).
• Hester v. United States, 265 U.S. 57: Cited as establishing that an open field is not a constitutionally protected area, contrasting with the telephone booth. Also cited regarding the limits of the trespass doctrine.
• Lewis v. United States, 385 U.S. 206: Cited for the principle that what a person knowingly exposes to the public is not protected by the Fourth Amendment.
• Rios v. United States, 364 U.S. 253: Cited for the proposition that what one seeks to preserve as private, even in a publicly accessible area (like a taxicab), may be constitutionally protected.
• Wong Sun v. United States, 371 U.S. 471: Cited for the requirement that the impartial judgment of a judicial officer must be interposed between the citizen and the police.
• Beck v. Ohio, 379 U.S. 89: Quoted for the principle that omitting prior authorization bypasses safeguards and relies on hindsight judgment.

• U.S. Constitution, Fourth Amendment: The core provision analyzed, guaranteeing the right against unreasonable searches and seizures and requiring warrants based on probable cause.
• 18 U.S.C. § 1084: The federal statute petitioner was charged with violating (transmitting wagering information by wire communication across state lines).
• 47 U.S.C. § 409(l): Cited in a footnote regarding a grant of immunity compelling testimony, deemed irrelevant to the disposition of the Fourth Amendment issue.
• Federal Rules of Criminal Procedure, Rule 41(d): Cited in a footnote regarding the requirement to serve a copy of the warrant, noting it doesn't invariably require service before the search.