In ancient Rome, the gens (pl. gentes) was a clan, or group of families, that shared a common name (the nomen) and a belief in a common ancestor. In the Roman naming convention, the second name was the name of the gens to which the person belonged.

The origins of the gentes are unclear, although they are probably not as ancient as the Romans themselves thought; although some were associated with particular cults or ceremonies, all were primarily personal and familial in nature, with no specific political or public duties. Also, the gentes did not usually have legendary founders that were worshipped, and the gentile assemblies are not recorded to have passed any sort of legally binding resolutions.

Nevertheless, the relationships of the gentes was a major factor in politics; members of the same gens were "family", and therefore frequently (thought not always) political allies.

Originally the plebeians and patricians were not allowed to intermarry, and several patrician families had collapsed as a result, until the Lex Canuleia was passed.

Among the patrician gentes there were two categories, the gentes maiores, and the gentes minores. The maiores were the leading families of Rome: these were the Aemilii, Claudii, Cornelii, Fabii, and Valerii, and they claimed special privileges both religious and secular.