The gens Cominia was a plebeian family at ancient Rome, known from the earliest days of the Republic. The first member of the family known to history was Postumus Cominius Auruncus, consul in 501 B.C., and from this it is generally inferred that the gens was originally patrician; but all of the later Cominii known to history were plebeians.
The surname Auruncus, borne by the consul of 501 B.C., suggests that the Cominii might have been of Auruncan origin, although if this were so, the family had reached the highest level of Roman society by the beginning of the Republic. However, there could be other explanations for this cognomen. This early consulship implies that the family was once numbered amongst the patricians, although in the later Republic all of the Cominii seem to have been plebeians. It may be that the family passed over to the plebeians during the fourth or fifth centuries B.C., or that the patrician branch of the gens became extinct. Alternatively it has been suggested that the earliest consuls included members of a number of plebeian families, and that plebeians were not formally excluded from the office until the passage of the Twelve Tables in 450-449 B.C. Valerius Maximus further suggests that the name of Auruncus is uncertain, and that he might instead have belonged to the gens Postumia, although most sources continue to regard Postumus as his praenomen.
The Cominii used the praenomina Postumus, Lucius, Sextus, Publius, Gaius, and Quintus. Of these it has been suggested that Postumus is a mistake for the nomen Postumius, but Postumus was an ancient praenomen, and was probably used by the early generations of this family.