Neptune (Latin: Neptūnus [nɛpˈtuːnʊs]) is the god of freshwater and the sea in Roman religion. He is the counterpart of the Greek god Poseidon. In the Greek-influenced tradition, Neptune is the brother of Jupiter and Pluto; the brothers preside over the realms of Heaven, the earthly world, and the Underworld. Salacia is his wife.

Depictions of Neptune in Roman mosaics, especially those of North Africa, are influenced by Hellenistic conventions. Neptune was likely associated with fresh water springs before the sea. Like Poseidon, Neptune was worshipped by the Romans also as a god of horses, under the name Neptunus Equester, a patron of horse-racing.