The Catuvellauni (Common Brittonic: *Catu-wellaunī, "war-chiefs") were a Celtic tribe or state of southeastern Britain before the Roman conquest, attested by inscriptions into the 4th century.

They appear as one of the civitates of Roman Britain in Ptolemy's Geography in the 2nd century, occupying the town of Verlamion (modern St Albans) and the surrounding areas of Hertfordshire, Bedfordshire and southern Cambridgeshire.

Their territory was bordered to the north by the Iceni and Corieltauvi, to the east by the Trinovantes, to the west by the Dobunni and Atrebates, and to the south by the Regni and Cantiaci.

He appears to have expanded his power at the expense of the Trinovantes to the east, as some of his coins, ca 15–10 BC, were minted in their capital Camulodunum (modern Colchester).

The grave of the "Druid of Colchester" dates to this period, providing evidence of medical practices and technology within the Catuvellauni tribe.

Adminius, whose power-base appears from his coins to have been in Kent, was exiled by his father shortly before AD 40 according to Suetonius, prompting the emperor Caligula to mount his abortive invasion of Britain.

It was the exile of the Atrebatic king, Verica, that prompted Claudius to launch a successful invasion, led by Aulus Plautius, in AD 43.

An inscription records that the civitas of the Catuvellauni were involved in the reconstruction of Hadrian's Wall, probably in the time of Septimius Severus in the early 3rd century.

The tombstone of a woman of the Catuvellauni called Regina, freedwoman and wife of Barates, a soldier from Palmyra in Syria, was found in the 4th-century Roman fort of Arbeia in South Shields in the northeast of England.