William Kidd, also known as Captain William Kidd or simply Captain Kidd (c.1645 23 May 1701), was a Scottish sea captain who was commissioned as a privateer and had experience as a pirate. He was tried and executed in London in 1701 for murder and piracy.

Kidd had captured a French ship, commanded by an English captain, as a prize. He had been commissioned by the Crown as a privateer for this expedition, but the political climate of England turned against him in this case. Some modern historians, for example Sir Cornelius Neale Dalton, deemed his piratical reputation unjust and said that he was acting as a privateer. Documents found in the early 20th century in London court papers supported Kidd's account of his actions.

Piracy is an act of robbery or criminal violence by ship or boat-borne attackers upon another ship or a coastal area, typically with the goal of stealing cargo and other valuable goods. Those who conduct acts of piracy are called pirates, while the dedicated ships that pirates use are called pirate ships. The earliest documented instances of piracy were in the 14th century BC, when the Sea Peoples, a group of ocean raiders, attacked the ships of the Aegean and Mediterranean civilizations. Narrow channels which funnel shipping into predictable routes have long created opportunities for piracy, as well as for privateering and commerce raiding. Historic examples include the waters of Gibraltar, the Strait of Malacca, Madagascar, the Gulf of Aden, and the English Channel, whose geographic structures facilitated pirate attacks. Privateering uses similar methods to piracy, but the captain acts under orders of the state authorizing the capture of merchant ships belonging to an enemy nation, making it a legitimate form of war-like activity by non-state actors. A land-based parallel is the ambushing of travelers by bandits and brigands in highways and mountain passes.While the term can include acts committed in the air, on land (especially across national borders or in connection with taking over and robbing a car or train), or in other major bodies of water or on a shore, in cyberspace, as well as the fictional possibility of space piracy, it generally refers to maritime piracy. It does not normally include crimes committed against people traveling on the same vessel as the perpetrator (e.g. one passenger stealing from others on the same vessel). Piracy or pirating is the name of a specific crime under customary international law and also the name of a number of crimes under the municipal law of a number of states. In the early 21st century, seaborne piracy against transport vessels remains a significant issue (with estimated worldwide losses of US$16 billion per year in 2004), particularly in the waters between the Red Sea and Indian Ocean, off the Somali coast, and also in the Strait of Malacca and Singapore.

Presently, pirates armed with automatic weapons, such as assault rifles, and machine guns, grenades and rocket propelled grenades use small motorboats to attack and board ships, a tactic that takes advantage of the small number of crew members on modern cargo vessels and transport ships. They also use larger vessels, known as "mother ships", to supply the smaller motorboats. The international community is facing many challenges in bringing modern pirates to justice, as these attacks often occur in international waters. Some nations have used their naval forces to protect private ships from pirate attacks and to pursue pirates, and some private vessels use armed security guards, high-pressure water cannons, or sound cannons to repel boarders, and use radar to avoid potential threats.

A romanticized version of piracy in the Age of Sail has long been a part of western pop culture. Captain Charles Johnson's A General History of the Pyrates, published in London in 1724, contained biographies of several pirates of the "golden age" and brought them to public attention. Pirates of the era have been further popularized and stereotyped by many subsequent works of fiction, most notably by the novels Treasure Island (1883) and Peter Pan (1911), two film adaptions of Treasure Island (1934 and 1950) and, more recently, by the Pirates of the Caribbean film franchise, which began in 2003.