Flaccus was a Roman cognomen of the plebeian Fulvii, considered one of the most illustrious gentes of the city. Cicero and Pliny state that the family was originally from Tusculum, and that members still lived there in the 1st century.

As usual for cognomina, "Flaccus" was likely originally a nickname, probably of Marcus Fulvius Flaccus, the founder of the family. It has been variously interpreted as meaning "big ears", "flop ears", "floppy", or "fatty".

• Marcus Fulvius Flaccus, consul 264 BC
• Lucius Valerius M.f. Flaccus, consul 262 BC
• Quintus Fulvius M.f. Flaccus, consul 237 BC, 224 BC, 212 BC, 209 BC
• Gnaeus Fulvius Flaccus, brother of Q. Fulvius, convicted of cowardice against Hannibal in 210 BC and exiled to Tarquinii
• Publius Valerius L.f. Flaccus, consul 227 BC
• Lucius Valerius Flaccus, consul with Cato 195 BC
• Flaccus, composer (second century BC)
• Q. Fulvius Cn.f. Flaccus, suffect consul 180 BC
• Quintus Fulvius Q.f. Flaccus, consul 179 BC
• Lucius Valerius Flaccus, consul 152 BC, 131 BC
• Servius Fulvius Flaccus, consul 135 BC
• Gaius Fulvius Flaccus, consul 134 BC
• Marcus Fulvius Flaccus, consul 125 BC
• Lucius Valerius Flaccus, consul 100 BC
• Lucius Valerius Flaccus, aedile 98 BC
• Gaius Valerius Flaccus, consul 93 BC
• Lucius Valerius Flaccus, urban praetor 63 BC
• Quintus Horatius Flaccus (Horace)
• Gaius Norbanus Flaccus, consul 38 BC, 24 BC, 15(?)
• Verrius Flaccus, freedman scholar
• Lucius Pomponius Flaccus, consul 15
• Aulus Avilius Flaccus, prefect of Egypt 32
• Aulus Persius Flaccus (34-62), poet
• Marcus Hordeonius Flaccus, commander of the Rhine legions during the Batavian rebellion, killed 70 AD
• Gaius Valerius Flaccus (1st century), poet
• C. Bellicius Flaccus Torquatus Tebanianus, consul 124, 143(?)
• Q. Uolusius Flaccus Cornelianus, consul 174