Pirates with commissions from a government are called privateers or corsairs, which comes from the mediaeval Latin cursa, "raid, expedition, inroad".

A privateer or corsair was similar in method to flibustiers but had a commission or a letter of marque from a government or king to capture merchant ships belonging to an enemy nation. It was paid with a substantial share of whatever they could capture from enemy ships and settlements, the rest going to the crown.The famous Barbary Corsairs of the Mediterranean were privateers, as were the Maltese Corsairs, who were authorized by the Knights of St. John.

In the Caribbean the use of privateers was especially popular. The cost of maintaining a fleet to defend the colonies was beyond national governments of the 16th and 17th centuries. Privateers would operate independently or as a fleet and if successful the rewards could be great — when Francis Drake captured the Spanish Silver Train at Nombre de Dios (Panama's Caribbean port at the time) in 1573 his crews were rich for life. This substantial profit made privateering something of a regular line of business; wealthy businessmen or nobles would be quite willing to finance this legitimized piracy in return for a share. The sale of captured goods was a boost to colonial economies as well.

The letter of marque was recognized by convention and meant that a privateer could not be charged with piracy although this was often not enough to save them; whether one was considered a pirate or a legally operating business often depended on whether you were the commissioning country or the object of attack. Seven nations agreed to suspend the use of the letter of marque under the Declaration of Paris of 1854, and others followed in the Hague Conventions. The most famous privateer was Sir Francis Drake and England was the main nation in promoting them.