A three-decker is a sail warship which carried her guns on three fully-armed decks. Usually additional guns were carried on the upper works (forecastle and quarterdeck) but this was not a continuous battery and so did not count. Three-deckers were usually ships of the line, classed as first-rate or second-rate.

The term three-decker was also often used to refer to a three-volume novel, the standard form for publishing English-language novels from about the 1830s to 1880s.

Ship types | Books