In Roman mythology, Quirinus was an early god of the Roman state. In Augustan Rome, Quirinus was also an epithet of Janus, as Janus Quirinus. His name is derived from Quiris meaning "spear."

Quirinus was originally most likely a Sabine god of war. The Sabines had a settlement near the eventual site of Rome, and erected an altar to Quirinus on the Collis Quirinalis, the Quirinal Hill, one of the Seven Hills of Rome. When the Romans settled there, they absorbed the cult of Quirinus into their early belief system — previous to direct Greek influence — and by the end of the first century BC Quirinus was considered to be the deified Romulus. He soon became an important god of the Roman state, being included in the earliest precursor of the Capitoline Triad, along with Mars (then an agriculture god) and Jupiter. Varro notes the Capitolium Vetus an earlier cult sited on the Quirinal, devoted to Jupiter, Juno and Minerva, among whom Martial makes a distinction between the "old Jupiter" and the "new".

In later times, however, Quirinus became far less important, losing his place to the later, more widely known Capitoline Triad (Juno and Minerva took his and Mars' place). Later still, Romans began to drift away from the state belief system in favor of more personal and mystical cults (such as those of Bacchus, Cybele, and Isis). In the end, he was worshiped almost exclusively by his flamen, the Flamen Quirinalis, who remained, however, one of the patrician flamines maiores, the "greater flamens" who preceded the Pontifex Maximus in precedence.