A mothership is a vessel or aircraft that carries a smaller vessel or aircraft that operates independently from it. Examples include bombers converted to carry experimental aircraft to altitudes where they can conduct their research, or ships that carry small submarines to an area of ocean to be explored. The mothership may also recover the smaller craft, or may go its own way after releasing it.

The term has achieved prominence in science fiction and in UFO lore, which extend the idea to apply to spaceships serving as the heart of a fleet. The concept of mothership clearly implies that the other ships in the fleet are dependent on the mothership for at least some services. Typically, a mothership will take up station in an area and remain there for long periods, while smaller ships sortie to interesting destinations. Sometimes a mothership is large enough to operate alone, or is so huge that it contains a fleet in its body.

Roles played in a fleet by a mothership may include:

• in-flight construction of new, smaller ships
• supply and repair tender
• troop transport
• carrier (of fighters, shuttles, etc.)
• supplementary propulsion (i.e., multi-ship warp field, hyperdrive, etc.)

Examples of motherships include:

• The gigantic 3 mile wide mothership in the 1983 mini-series V
• Star Trek vessels, which serve as motherships to their shuttlepods and sometimes to fighter craft
• The mothership in the Homeworld computer game
• The Galactica ship of Battlestar Galactica, which is a mothership to colonial fighter craft
• The Mon Calamari cruisers of the rebels and the imperial star destroyers are some of the many motherships in the Star Wars movies
• The ill-fated Discovery in 2001: A Space Odyssey is the mothership to 3 service and exploration pods
• The huge mothership in Close Encounters of the Third Kind
• The alien mothership in Independence Day