A Dutch Merchantman Attacked by an English Privateer, off La Rochelle by Cornelis Claesz van Wieringen, 1616. Repro ID: BHC0723 ©National Maritime Museum, Greenwich, LondonA letter of marque was a commission issued by the High Court of Admiralty authorizing privately owned ships (known as privateers) to capture enemy merchant ships.

The earliest letter of marque was issued in 1293 and they continued to be issued in times of war until privateering was abolished in 1856.

Records relating to letters of marque and privateers are within the High Court of Admiralty records held by The National Archives.