In admiralty law prizes are equipment, vehicles, vessels, and cargo captured during armed conflict. The most common use of prize in this sense is the capture of an enemy ship and its cargo as a prize of war. In the past, the capturing force would commonly be allotted a share of the worth of the captured prize. Nations often granted letters of marque that would entitle private parties to capture enemy property, usually ships. Once the ship was secured on friendly territory, it would be made the subject of a prize case: an in rem proceeding in which the court determined the status of the condemned property and the manner in which the property was to be disposed of.

A letter of marque and reprisal was a government license in the Age of Sail that authorized a private person, known as a privateer or corsair, to attack and capture vessels of a nation at war with the issuer. After capturing, the privateers could bring the case of that prize before their own admiralty court for condemnation and transfer of ownership to the privateer. A letter of marque and reprisal would include permission to cross an international border to conduct a reprisal and was authorized by an issuing jurisdiction to conduct reprisal operations outside its borders.