Hijacking, the forcible seizure of an aircraft, ship, train, or motor vehicle in transit. The robbery of passengers or of a vehicle's goods without taking the vehicle itself is also known as hijacking. The crime of hijacking an ocean vessel is known as piracy. Airplane hijacking often is called air piracy, or skyjacking; the hijacking of an automobile is commonly called carjacking.

The term hijacking came into use in the Prohibition era, 1920–33, when it referred to the theft by bootleggers of a rival's truck-loads of liquor. Gradually the term took on a broader meaning. There was extensive hijacking of airplanes during the 1960's, sometimes as a means of blackmail or for the purpose of being transported to another country. The crime was curbed in the United States by stringent passenger-screening procedures but remained a problem elsewhere. Beginning in the 1970's, skyjacking became a tactic of international political terrorists. Carjacking, most commonly occurring at intersections, became a problem in the 1990's in some American cities. On September 11, 2001, about 3,000 people died as a result of the worst skyjacking incident in U.S. history. Terrorists in hijacked commercial airplanes deliberately crashed into the two towers of the World Trade Center in New York City and into the Pentagon Building outside Washington, D.C. Later that day, another hijacked plane crashed in Somerset County, Pennsylvania.