In law, a warrant can mean any form of authorization. Often in statute, the warrant of a particular person is required before certain administrative actions can take place. For example, before the United States Secretary of State may affix the Great Seal of the United States to letters patent, the president must give authorization. Warrant officers derive their authority from an authorization given by a defense minister as opposed to actually being an officer of the state.

Most often, the term warrant refers to a specific type of authorization; a writ issued by a competent officer, usually a judge or magistrate, which commands an otherwise illegal act that would violate individual rights and affords the person executing the writ protection from damages if the act is performed. The Fourth Amendment to the United States Constitution prohibits search or arrest without a warrant, unless there is a reasonable doubt to privacy.

Warrants are typically issued by courts and are directed to the sheriff or a police officer. The warrants issued by a court normally are search warrants, arrest warrants, and execution warrants. A typical arrest warrant in the United States will take the approximate form of:

"This Court orders the Sheriff to find the named person, wherever he may be found, and deliver said person to the custody of the Court."

Warrants are also issued by other government entities, particularly legislatures, since most have the power to compel the attendance of their members. This is called a call of the house.