A privateer is a private person or vessel which engages in commerce raiding under a commission of war. Since robbery under arms was a common aspect of seaborne trade, until the early 19th century all merchant ships carried arms. A sovereign or delegated authority issued commissions, also referred to as letters 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 crews prisoner for exchange. Captured ships were subject to condemnation and sale under prize law, with the proceeds divided by percentage between the privateer's sponsors, shipowners, captains and crew. A percentage share usually went to the issuer of the commission (i.e. the sovereign). Most colonial powers, as well as other countries, engaged in privateering.
Privateering allowed sovereigns to augment their naval forces at relatively low cost by mobilizing privately owned armed ships and sailors to supplement state power. For participants, privateering provided the potential for a greater income and profit than obtainable as a merchant seafarer or fisher while avoiding the dangers associated with outright piracy. However, the line between privateers and pirates was not always clear.
