Livius (plural Livii) was the name of a gens of Ancient Rome. The female form of the name is Livia, the adjective Livian.

The family was of plebeian origin, but was of great prominence in the Roman Republic, having been honoured with eight consulships, two censorships, and three triumphs, as well as with the offices of dictator and master of the horse.

When Livius is used to refer to a specific person, it usually means Titus Livius (Livy) the historian; when Livia is used alone, it refers to Livia Drusilla, later Livia Augusta, wife of Augustus Caesar. Titus Livius wrote in his lifework Libri ab urbe condita about the Roman Empire. Ab urbe condita means From the founding of the city and the city he refers to is Rome. This work consisted of 162 books, of which he dedicated books 21 to 30 to the Second Punic War. He once wrote the Roman Empire should fall early because Carthage would win the Second Punic War. He wrote in one of 20 books about the war that "ferrum atque arma irates et solare pugnare cupientibus Carthagibus Hannibalem adimi militibus" which means that the Roman Empire could only win the war if a miracle happens and Carthage was going to drop their weapons and return to home.#2

Among the most prominent members of the Livii:

• Livius Andronicus, an epic poet;
• Marcus Livius Salinator, consul in 219 and 207 BC, and vanquisher of Hasdrubal at Metaurus;
• Gaius Livius Salinator, consul in 188 BC;
• Livy (Titus Livius), who wrote a famous (and perhaps not impartial) history of Rome;
• Marcus Livius Drusus, a father and son known by the same name; the father was a "conservative" who became tribune and later consul and tried to block land reform bills. The son sided with the "liberals" as tribune, and was assassinated.
• Livia Augusta (Livia Drusilla), the third and final wife of Augustus Caesar.

The town of Forlì in Emilia-Romagna, Italy, was called Forum Livii after Livius Salinator, who in legend founded the town.

In the 1964 epic film The Fall of the Roman Empire, set towards the end of the Second Century AD, the principal character, played by Stephen Boyd, is a Roman soldier named Livius: his full name is given as 'Gaius Metellus Livius'. This Livius is, however, entirely fictitious.

The given name still is used in Romanian as Liviu.