In ancient Roman religion, Inuus (Classical Latin: [ˈɪnuʊs]) was a god, or aspect of a god, who embodied sexual intercourse. The evidence for him as a distinct entity is scant. Maurus Servius Honoratus wrote that Inuus is an epithet of Faunus (Greek Pan), named from his habit of intercourse with animals, based on the etymology of ineundum, "a going in, penetration," from inire, "to enter" in the sexual sense. Other names for the god were Fatuus and Fatuclus (with a short a).

Walter Friedrich Otto disputed the traditional etymology and derived Inuus instead from in-avos, "friendly, beneficial" (cf. aveo, "to be eager for, desire"), for the god's fructifying power.

Livy is the sole source for identifying Inuus as the form of Faunus for whom the Lupercalia was celebrated: "naked young men would run around venerating Lycaean Pan, whom the Romans then called Inuus, with antics and lewd behavior." Although Ovid does not name Inuus in his treatment of the Lupercalia, he may allude to his sexual action in explaining the mythological background of the festival. When Romulus complains that a low fertility rate has rendered the abduction of the Sabine women pointless, Juno, in her guise as the birth goddess Lucina, offers an instruction: "Let the sacred goat go into the Italian matrons" (Italidas matres … sacer hirtus inito, with the verb inito a form of inire). The would-be mothers recoil from this advice, but an augur, "recently arrived from Etruscan soil," offers a ritual dodge: a goat was killed, and its hide cut into strips for flagellating women who wished to conceive; thus the aetiology for the practice at the Lupercalia. Rutilius Namatianus offers a similar verbal play, Faunus init ("Faunus enters"), in pointing out a statue depicting the god at Castrum Inui ("Fort Inuus"). Georg Wissowa rejected both the etymology and the identification of Inuus with Faunus.

The scant evidence for Inuus has not been a bar to elaborate scholarly conjecture, as William Warde Fowler noted at the beginning of the 20th century in his classic work on Roman festivals. "It is quite plain," Fowler observed, "that the Roman of the literary age did not know who the god (of the Lupercalia) was."

Servius's note on Inuus is prompted by the mention of Castrum Inui at Aeneid 6.775:

This is one and the same as the town (civitas) in Italy which is called New Fort (Castrum Novum). Vergil says 'Fort Inuus' for the place, that is, 'Fort Pan', who has a cult there. He is called Inuus, however, in Latin, Πάν (Pan) in Greek; also Ἐφιάλτης (Ephialtes), in Latin Incubus; likewise Faunus, and Fatuus, Fatuclus. He is called Inuus, however, from going around having sex everywhere with all the animals, hence he is also called Incubus.

Castrum Novum is most likely Giulianova on the coast of Etruria, but Servius seems to have erred in thinking that Castrum Inui, on the coast of Latium, was the same town.

Rutilius makes the same identification as Servius but explains that there was a stone carving of Inuus over the gate of the town. This image, worn by time, showed horns on its "pastoral forehead", but the ancient name was no longer legible. Rutilius is noncommittal about its identity, "whether Pan exchanged Tyrrhenian woodlands for Maenala, or whether a resident Faunus enters (init) his paternal retreats," but proclaims that "as long as he revitalizes the seed of mortals with generous fertility, the god is imagined as more than usually predisposed to sex."