Hijacking or highjacking is the forcible robbery from, or seizure of a vehicle in transit. Historically the term used to refer to robbery of trucks, other land motor vehicles car jacking and aircraft skyjacking. Contemporarily the term is primarily associated with high-profile aircraft hijacking for political purposes including terrorism, although other cases have included the cruise ship Achille Lauro in 1985 which could also be considered piracy.

The term "hijacking" is also used when spyware or a virus writes itself in a computer program in such a way that whenever that program starts to work, besides its normal duties it does other things too, which the creator of the virus or spyware meant it to.