A privateer or corsair used similar methods to a pirate, but acted while in possession of a commission or letter of marque from a government or monarch authorizing the capture of merchant ships belonging to an enemy nation. For example, the United States Constitution of 1787 specifically authorized Congress to issue letters of marque and reprisal. The letter of marque was recognized by international convention and meant that a privateer could not technically be charged with piracy while attacking the targets named in his commission. This nicety of law did not always save the individuals concerned, however, as whether one was considered a pirate or a legally operating privateer often depended on whose custody the individual found himself in--that of the country that had issued the commission, or that of the object of attack. Spanish authorities were known to execute foreign privateers with their letters of marque hung around their necks to emphasize Spain's rejection of such defenses. Furthermore, many privateers exceeded the bounds of their letters of marque by attacking nations with which their sovereign was at peace (Thomas Tew and William Kidd are notable examples), and thus made themselves liable to conviction for piracy. However, a letter of marque did provide some cover for such pirates, as plunder seized from neutral or friendly shipping could be passed off later as taken from enemy merchants.
The famous Barbary Corsairs of the Mediterranean were privateers, as were the Maltese Corsairs, who were authorized by the Knights of St. John, and the Dunkirkers in the service of the Spanish Empire. From 1609 to 1616, England lost 466 merchant ships to Barbary pirates. One famous privateer was Sir Francis Drake. His patron was Queen Elizabeth I, and their relationship ultimately proved to be quite profitable for England.
Privateers were a large proportion of the total military force at sea during the 17th and 18th centuries. During the Nine Years War, the French adopted a policy of strongly encouraging privateers, including the famous Jean Bart, to attack English and Dutch shipping. England lost roughly 4,000 merchant ships during the war. In the following War of Spanish Succession, privateer attacks continued, Britain losing 3,250 merchant ships. During the War of Austrian Succession, the Britain lost 3,238 merchant ships and France lost 3,434 merchant ships to the British.
During the King George's War, approximately 36,000 Americans served aboard privateers at one time or another. During the American Revolution, about 55,000 American seamen served aboard the privateers. The American privateers had almost 1,700 ships, and they captured 2,283 enemy ships. Between the end of the Revolutionary War and 1812, less than 30 years, the Britain, France, Naples, the Barbary States, Spain, and the Netherlands seized approximately 2,500 American ships. Payments in ransom and tribute to the Barbary states amounted to 20% of United States government annual revenues in 1800. Throughout the American Civil War, Confederate privateers successfully harassed Union merchant ships.
Privateering lost international sanction under the Declaration of Paris in 1856.