389 U.S. 347 (1967) (U.S. Supreme Court)
Katz v. United States transformed Fourth Amendment doctrine by shifting the focus from places and physical trespass to people and their privacy.
Does the warrantless electronic recording of a person's conversation from outside a public telephone booth, where the speaker has sought to preserve privacy, constitute a search and seizure in violation of the Fourth Amendment?
The Fourth Amendment protects people, not places. A search occurs when the government violates a person's subjective expectation of privacy that society recognizes as reasonable. Physical trespass is not required. Absent a specifically applicable exception, electronic surveillance of private conversations requires a warrant supported by probable cause and particularity.
Yes. The government's warrantless electronic eavesdropping on Katz's conversation in a closed public phone booth violated the Fourth Amendment. The conviction was reversed.
Katz is the cornerstone of modern Fourth Amendment law. It recast the definition of a search in terms of reasonable expectations of privacy, enabling the Constitution to regulate emerging forms of surveillance without requiring a physical trespass. The decision directly informs analysis of electronic eavesdropping and has been extended to technologies like thermal imaging (Kyllo v. United States) and cell-site location data (Carpenter v. United States). At the same time, Katz coexists with doctrines limiting privacy expectations, such as the third-party doctrine (Smith v. Maryland; United States v. Miller), and with renewed attention to trespass as an additional, not exclusive, basis for finding a search (United States v. Jones). For law students, Katz provides the analytic template for Fourth Amendment questions: identify the individual's asserted privacy interest, assess whether the person exhibited a subjective expectation, evaluate whether that expectation is objectively reasonable, and determine whether a warrant or exception applies. It also influenced legislative responses, notably Title III of the Omnibus Crime Control and Safe Streets Act of 1968, which set procedures for wiretaps consistent with Katz's requirements.