Third-Party Doctrine

The third-party doctrine is a United States legal theory that holds that people who voluntarily give information to third parties—such as banks, phone companies, internet service providers (ISPs), and e-mail servers—have "no reasonable expectation of privacy." A lack of privacy protection allows the United States government to obtain information from third parties without a legal warrant and without otherwise complying with the Fourth Amendment prohibition against search and seizure without probable cause and a judicial search warrant. Libertarians typically call this government activity unjustified spying and a violation of individual and privacy rights.

Follow by the states in 1791, the Fourth Amendment to the United States Constitution was enacted in 1792, holding:

The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.

In Katz v. United States (1967), the United States Supreme Court established its reasonable expectation of privacy test. In 1976 (United States v. Miller) and 1979 (Smith v. Maryland), the Court affirmed that "a person has no legitimate expectation of privacy in information he voluntarily turns over to third parties."

In response to Katz v. United States (1967) and Berger v. New York (1967), the United States Congress enacted the Omnibus Crime Control and Safe Streets Act of 1968, of which Title III is known as the "Wiretap Act." Title III was Congress' attempt to extend Fourth Amendment-like protections to telephonic and other wired forms of communication.

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