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A warrant is generally an order that serves as a specific type of authorization, that is, a writ issued by a competent officer, usually a judge or magistrate, which permits an otherwise illegal act that would violate individual rights and affords the person executing the writ protection from damages if the act is performed.
A warrant is usually issued by a court and is directed to a sheriff, a constable, or a police officer. Warrants normally issued by a court include search warrants, arrest warrants, and execution warrants.
In the United Kingdom, senior public appointments are made by warrant under the royal sign-manual, the personal signature of the monarch, on the recommendation of the government. In an interesting survival from medieval times, these warrants abate (lose their force) on the death of the sovereign if they have not already been executed. This particularly applied to death warrants in the days when England authorized capital punishment. Perhaps the most celebrated example of this occurred on 17 November 1558, when several Protestant heretics were tied to their stakes in Smithfield, and the firewood bundles were about to be lit when a royal messenger rode up to announce that Mary I had died and that the warrants had lost their force. The first formal act of Mary's successor, Elizabeth I, was to decline to re-issue the warrants, and the heretics were released a few weeks later.
For many years, the English, later British, government had used a "general warrant" to enforce its laws. These warrants were broad in nature and did not have specifics as to why they were issued or what the arrest was being made for. A general warrant placed almost no limitations on the search or arresting authority of a soldier or sheriff. This concept had become a serious problem when those in power issued general warrants to have their enemies arrested when no wrongdoing had been done. The Parliament of Great Britain,  passed the Revenue Act of 1767,  which reaffirmed the legality of writs of assistance, or general search warrants, and gave customs officials broad powers to search houses and businesses for smuggled goods.  This law was one of the key acts of the United Kingdom which led to the American Revolution, and is the direct reason that the American Founding Fathers ensured that general warrants would be illegal in the United States by ratifying the Fourth Amendment to the U.S. Constitution in 1791.
Under the Fourth Amendment to the United States Constitution a warrant is broadly required which particularly describes the place to be searched, and the persons, or things, to be seized; and no warrants shall be issued, but upon probable cause, supported by testimony before a judge.
The courts have recognized many exceptions to the warrant requirement, including exceptions for routine administrative or inventory searches, searches made under exigent circumstances, and searches made with consent. 
A typical arrest warrant in the United States will take the approximate form of: "This Court orders the Sheriff or Constable to find the named person, wherever he may be found, and deliver said person to the custody of the Court." Generally, a U.S. arrest warrant must contain the caption of the court issuing the warrant, the name (if known) of the person to be arrested, the offense charged, the date of issue, the officer(s) to whom the warrant is directed, and the signature of the magistrate.  Warrants may also be issued by other government entities, including legislatures, since most have the power to compel the attendance of their members. When a legislature issues a warrant, it is called a call of the house.
The person being investigated, arrested, or having their property seized, pursuant to a warrant is given a copy of the warrant at the time of its execution.
- Arrest warrant, issued by a judge to detain someone
- Warrant of committal, issued by a judge ordering enforcement of a previous order against an uncooperative person or corporation
- Warrant of delivery, civil writ issued by a judge ordering property delivered to a named person
- Warrant of execution, writ issued by a judge allowing law enforcement officers to seize property
- Execution warrant, writ issued by a judge authorizing the death of someone
- Warrant of possession, Australian judge order to terminate a residential real estate tenancy
- Possessory warrant, civil writ issued by a judge ordering property delivered to a named person
- Search warrant, writ issued by a judge allowing law enforcement officers to look inside a property
- Arrest Warrant of 11 April 2000 case
- Warrant canary, a method used by Internet service providers to inform their customers that the provider has not been served with a secret government subpoena
- Quo warranto, a writ requiring the person to whom it is directed to show what authority they have for exercising some right or power (or "franchise") they claim to hold
- The Treaty (act) of the Union of Parliament 1706, Scots History Online
- The Revenue Act of 1767 was 7 Geo. III ch. 46; Knollenberg, Growth, 47; Labaree, Tea Party, 270n12. It is also known as the Townshend Revenue Act, the Townshend Duties Act, and the Tariff Act of 1767.
- Reid, Rebellious Spirit, 29, 135n24.
- Larson, Aaron (2 February 2017). "What Are Your Fourth Amendment Rights". ExpertLaw. Retrieved 20 July 2017.
- Criminal Procedure for the Criminal Justice Professional; John N. Ferdico, Henry Fradella, Christopher Totten; Cengage Learning; 2015; page 246.
- Craies, William Feilden (1911). Encyclopædia Britannica. 28 (11th ed.). pp. 327–327. .
- UK appointments made by warrant under the Royal sign manual—from the London Gazette