A superstructure is an upward extension of an existing structure above a baseline. This term is applied to various kinds of physical structures such as buildings, bridges, or ships. The word "superstructure" is a combination of the Latin prefix, super, (meaning above, in addition) with the Latin stem word, structure, (meaning to build or to heap up).

In order to improve the response during earthquakes of buildings and bridges, the superstructure might be separated from its foundation by various civil engineering mechanisms or machinery. All together, these implement the system of earthquake protection called base isolation.

As stated above, superstructure consists of the parts of the ship or a boat, including sailboats, fishing boats, passenger ships, and submarines, that project above her main deck. This does not usually include its masts or any armament turrets. Note that in modern times, turrets do not always carry naval artillery, but they can also carry missile launchers and/or antisubmarine warfare weapons.