From that bold beginning developed a more specific expectation that government may search a person’s house, or personal papers, only with a valid reason (later, “probable cause”), legal authority (eventually in the form of a search warrant), and only after giving adequate notice before seeking entry or access.

Prominent among the principles that the U.S. Constitution’s framers felt imperative to embody in the Bill of Rights was that of privacy. The Fourth Amendment has for the past 212 years been the bulwark of such privacy protection. Most states have comparable provisions in their own constitutions, and in 1963 the U.S. Supreme Court declared that state and local governments are as fully bound to respect privacy as is the national government, since the due process clause of the Fourteenth Amendment incorporates or absorbs the basic safeguards of the Fourth and makes those safeguards fully applicable to official action at all levels.

Interpreting and applying the spare words of the Fourth Amendment have posed a major and continuing challenge for the courts. Indeed, hardly a term of the U.S. Supreme Court passes without at least one case on the docket that juxtaposes government’s need for information, usually pursuant to law enforcement investigation, and a citizen’s or organization’s wish to withhold that information, or to prevent government from gathering the information by invading premises or conducting surveillance in other forms.

The Supreme Court’s recognition of a citizen’s right to be secure against unauthorized government intrusion dates at least to a batch of cases in the 1880s, beginning with Kilbourn v. Thompson, 103 U.S. 168, 190 (1880), noting that Congress does not “possess the general power of making inquiry into the private affairs of the citizen.” Later rulings extended the same principle to inquiries by federal administrative agencies. In 1886, in Boyd v. United States, 116 U.S. 616, 530 (1886), the Court struck down a regulatory measure that it found unduly intrusive into “the sanctity of a man’s home and the privacies of life.”

The later evolution of Fourth Amendment privacy guarantees highlights several notable 20th-century decisions. While the Court ruled in Olmstead v. United States, 277 U.S. 438 (1928), that the use of a wiretap did not violate the Fourth Amendment because there had been no physical invasion of a citizen’s home, person, or papers, later judgments importantly qualified the potential scope of that decision. Notably, the Court held in Katz v. United States, 389 U.S. 347 (1967), that privacy rights did extend to a telephone booth, noting that “wherever a man may be, he is entitled to know that he will remain free from unreasonable searches and seizures.”

The Supreme Court has dealt extensively in the last half century with conditions and circumstances under which searches of automobiles,



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