A privateer is a private person or ship that engages in maritime warfare under a commission of war. Because of the high level of piracy and impressment, merchant ships where armed. A sovereign or delegated authority issued commissions, also referred to as a letter of marque, during wartime. The commission empowered the holder to carry on all forms of hostility permissible at sea by the usages of war. This included attacking foreign vessels and taking them as prizes, and taking prize crews as prisoners for exchange. Captured ships were subject to condemnation and sale under prize law, with the proceeds divided by percentage between the privateer's sponsors, ship owners, captains and crew. A percentage share usually went to the issuer of the commission (i.e. the sovereign).
Privateering allowed sovereigns to raise revenue for war by mobilizing privately owned armed ships and sailors to subsidize state power. For participants, privateering provided the potential for a greater income and profit than obtainable as a merchant seafarer or fisher.