The gens Petronia was a plebeian family at ancient Rome. This gens claimed an ancient lineage, as a Petronius Sabinus is mentioned in the time of Lucius Tarquinius Superbus, the last of the Roman kings, but few Petronii are mentioned in the time of the Republic. They are frequently encountered under the Empire, holding numerous consulships, and eventually obtaining the Empire itself during the brief reign of Petronius Maximus in AD 455.

The Petronii were of Sabine origin, as indicated by the surname Sabinus, belonging to the legendary figure from the time of Tarquin, and alluded to by coins minted by Publius Petronius Turpilianus, depicting the death of Tarpeia, whom according to legend was persuaded by the Sabines under Titus Tatius to open the citadel to them, in the time of Romulus. The nomen Petronius appears to be a patronymic surname derived from the Oscan praenomen Petro or Petrus, the Oscan equivalent of the Latin Quartus, fourth, and making Petronius cognate with a number of obscure Latin gentilicia, such as Quartius and Quartinius. An alternative derivation would be from the cognomen Petrus, a rustic, although this may also derive from the Oscan praenomen. Petronius belongs to a large class of gentilicia derived from other names ending in -o, most of which are plebeian.

The early Petronii used the praenomina Gaius, Marcus, and Publius, all of which were very common throughout Roman history. Other names occur toward the end of the second century AD, including Quintus, Lucius, and Sextus, but these may have been inherited from other families.