The gens Manilia was a plebeian family at Rome. Members of this gens are frequently confused with the Manlii, Mallii, and Mamilii. Several of the Manilii were distinguished in the service of the Republic, with Manius Manilius obtaining the consulship in 149 BC; but the family itself remained small and relatively unimportant.
The nomen Manilius seems to be derived from the praenomen Manius, and so probably shares a common root with the nomen of the Manlii. This being the case, the Manilii were almost certainly of Latin origin.
The Manilii were never divided into distinct families, and the only surname found under the Republic is Mancinus, although this probably belonged to one of the Manlii, who has been erroneously named as a Manilius in some manuscripts. A few cognomina are found in Imperial times.