Fourth Amendment Law and Legal Definition

The Fourth Amendment to the U.S Constitution is part of the Bill of Rights which protects citizens against unreasonable searches and seizures. It requires search and arrest warrants to be judicially approved, supported by probable cause, and the warrant must describe with particularity "the place to be searched, and the persons or things to be seized" and be supported by "oath or affirmation" of the officer requesting its issuance. However, there are exceptions and not every search, seizure, or arrest must be made pursuant to a lawfully executed warrant.

The U.S. Supreme Court of the United States has held that the Fourth Amendment is applicable to state governments under the Due Process Clause of the Fourteenth Amendment. Additionally, all state constitutions contain a similar provision.

The Fourth Amendment only protects against searches and seizures conducted by the government or pursuant to governmental direction. Surveillance and investigatory actions taken by strictly private persons, such as private investigators, suspicious spouses, or neighbors, are not governed by the Fourth Amendment. However, Fourth Amendment concerns do arise when those same actions are taken by a law enforcement official or a private person working in conjunction with law enforcement. Even if governmental action is involved, the Fourth Amendment does not apply unless defendants first establish that they had a reasonable expectation of privacy in the place to be searched or the thing to be seized.