National Steel and Shipbuilding Company, commonly referred to as NASSCO, is an American shipbuilding company with four shipyards located in San Diego, Norfolk, Bremerton, and Mayport. It is a division of General Dynamics. NASSCO owns a subsidiary manufacturing facility with TIMSA in Mexicali, Mexico. The San Diego shipyard specializes in constructing commercial cargo ships and auxiliary vessels for the US Navy and Military Sealift Command; it is the only new-construction shipyard on the West Coast of the United States. NASSCO performs ship repairs and conversions for the United States Navy in all four shipyard locations: San Diego, Norfolk, Bremerton, and Mayport.

A shipyard, also called a dockyard or boatyard, is a place where ships are built and repaired. These can be yachts, military vessels, cruise liners or other cargo or passenger ships. Compared to shipyards, which are sometimes more involved with original construction, dockyards are sometimes more linked with maintenance and basing activities. The terms are routinely used interchangeably, in part because the evolution of dockyards and shipyards has often caused them to change or merge roles.