A search warrant is a written warrant issued by a judge or magistrate which authorizes the police to conduct a search of a person or location for evidence of a criminal offense.

All jurisdictions with a rule of law and a right to privacy put constraints on the rights of police investigators, and typically require search warrants, or an equivalent procedure, for searches within a criminal enquiry. There typically also exist exemptions for "hot pursuit": if a criminal flees the scene of a crime and the police officer follows him, the officer has the right to enter an edifice in which the criminal has sought shelter.

Conversely, in authoritarian regimes, the police typically have the right to search property and people without having to provide justifications, or without having to secure an authorization from the judiciary.

United States

In the U.S. the issue of federal warrants is determined under Title 18 of the US Code. The law has been restated and extended under Rule 41 of the Federal Rules of Criminal Procedure . Each state also promulgates its own laws governing the issuance of search warrants.

Under the Fourth Amendment to the United States Constitution, most searches by the police require a search warrant. In order to obtain one, an officer must first prove that probable cause exists, although this can be based on hearsay evidence and can even be obtained by oral testimony given over a telephone. Both property and persons can be seized under a search warrant. Under the Fourth Amendment searches must be reasonable and specific. This means that a search warrant must be specific as to the specified object to be searched for and the place to be searched. Other items, rooms, outbuildings, persons, vehicles, etc. would require a second search warrant.

Section 213 of the USA PATRIOT Act authorizes "sneak and peek" warrants, which permit federal agents to enter a suspect's home or office and search for and seize items without notifying the suspect.