The
Fourth Amendment (
Amendment IV) to the
United States Constitution is part of the
Bill of Rights. It prohibits unreasonable
searches and seizures. In addition, it sets requirements for issuing
warrants: warrants must be issued by a judge or magistrate, justified by
probable cause, supported by oath or affirmation, and must particularly describe the place to be searched and the persons or things to be seized.
Fourth Amendment case law deals with three main issues: what government activities are "searches" and "seizures," what constitutes probable cause to conduct searches and seizures, and how violations of Fourth Amendment rights should be addressed. Early court decisions limited the amendment's scope to physical intrusion of property or persons, but with
Katz v. United States (1967), the
Supreme Court held that its protections extend to intrusions on the privacy of individuals as well as to physical locations. A warrant is needed for most search and seizure activities, but the Court has carved out a series of exceptions for
consent searches,
motor vehicle searches,
evidence in plain view,
exigent circumstances,
border searches, and other situations.
The
exclusionary rule is one way the amendment is enforced. Established in
Weeks v. United States (1914), this rule holds that
evidence obtained as a result of a Fourth Amendment violation is generally
inadmissible at criminal trials. Evidence discovered as a later result of an illegal search may also be inadmissible as "
fruit of the poisonous tree", unless it inevitably would have been discovered by legal means.
The Fourth Amendment was adopted in response to the abuse of the
writ of assistance, a type of general
search warrant issued by the
British government, and a major source of tension in
pre-Revolutionary America. The Fourth Amendment was introduced in Congress in 1789 by
James Madison, along with the other amendments in the Bill of Rights, in response to
Anti-Federalist objections to the new Constitution. Congress
submitted the amendment to the states on September 28, 1789. By December 15, 1791, the necessary three-fourths of the states had
ratified it. On March 1, 1792, Secretary of State
Thomas Jeffersonannounced that it was officially part of the Constitution.
Because the Bill of Rights did not initially apply to state or local governments, and federal criminal investigations were less common in the first century of the nation's history, there is little significant case law for the Fourth Amendment before the 20th century. The amendment was held to
apply to state and local governments in
Mapp v. Ohio (1961) via the
Due Process Clause of the
Fourteenth Amendment.
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