The gens Postumia was a noble patrician family at ancient Rome. Throughout the history of the Republic, the Postumii frequently occupied the chief magistracies of the Roman state, beginning with Publius Postumius Tubertus, consul in 505 BC, the fifth year of the Republic. Although like much of the old Roman aristocracy, the Postumii faded for a time into obscurity under the Empire, individuals bearing the name of Postumius again filled a number of important offices from the second century AD to the end of the Western Empire.^[2]

The nomen Postumius is a patronymic surname, derived from the praenomen Postumus, which presumably belonged to the ancestor of the gens. That name is derived from the Latin adjective, postremus, meaning "last" or "hindmost," originally indicating a last-born or youngest child. However, its meaning has long been confounded with that of posthumous, indicating a child born after the death of the father; this misunderstanding is fostered by the fact that a posthumous child is also necessarily the youngest.^[3]

The most prominent families of the Postumii during the early Republic favored the praenomina Aulus, Spurius, and Lucius, with Marcus, Publius, and Quintus receiving lesser use. Other names are occasionally found toward the end of the Republic, including Gaius, Gnaeus, and Titus.

The earliest family of the Postumii to occur in history bore the cognomen Tubertus, derived from tuber, a lump or swelling. But by far the greatest family of the Postumii bore the surname Albus, white, which in later generations became Albinus, whitish. This family flourished from the beginning of the Republic down to its end, in the first century BC, and for a century all of its members bore the agnomen Regillensis, in memory of the Battle of Lake Regillus, where the Roman dictator Aulus Postumius Albus won everlasting renown by defeating the Latin League, led by Octavius Mamilius and Lucius Tarquinius Superbus, the seventh and last King of Rome, and securing the future of the Republic.^{[lower-roman 1][2][4][5]}

In the later Republic other surnames are found among the Postumii, including Megellus; Pyrgensis, from the Etruscan city of Pyrgi; Tempsanus, from Temesa, a city of Magna Graecia; and Tympanus, from tympanum, a drum. A few of Postumii without cognomina are known from various sources.^[2][6][7]

This list includes abbreviated praenomina. For an explanation of this practice, see filiation.

This chart shows the probable descent of the Postumii Albini, from the sixth century BC to the end of the Republic. The chart is based on one found in the Realencyclopädie der Classischen Altertumswissenschaft.^[113]

• List of Roman gentes