Lutetia (sometimes Lutetia Parisiorum or Lucotecia, in French Lutèce) was a town in pre-Roman and Roman Gaul. It was located on what is now the Île de la Cité, an island on the river Seine, in the centre of the modern city of Paris. It was the chief settlement (or oppidum) of the Parisii, a Celtic people who settled in the area during the 3rd century BC.

The name of Lutetia was first recorded by Julius Caesar in his Commentaries on the Gallic Wars (notably in book 7, chapters 57-58). There are a number of explanations of its derivation. Some have suggested that it is derived from the Latin word lutum or "mud", which would give Lutetia Parisiorum the meaning of "mud town of the Parisii".

The town was captured by the Roman Empire in 52 BC during the conquest of Gaul. It was apparently already quite a prosperous place, as it occupied a very strategic position on the river and was able to control shipping in both directions. The Lutetians backed the revolt of Vercingetorix against the Romans under Caesar, reportedly contributing 8,000 men to Vercingetorix's army. It was garrisoned by Vercingetorix's lieutenant Camulogenus, whose army camped on the Mons Lutetius (where the Panthéon is now situated). The Romans crushed the rebels at nearby Melun and took control of Lutetia.

Under Roman rule, Lutetia was thoroughly Romanised and grew considerably to become a small city, with a population estimated at around 8,000 people. It did not have a great deal of political importance - the capital of its province, Lugdunensis Senona, was Agedincum (modern Sens, Yonne). It was Christianised in the 3rd century when St Denis became the city's first bishop. The process was not entirely peaceful - in about 250 St Denis and two companions were arrested and decapitated on the hill of Mons Mercurius, thereafter known as Mons Martis (Martyrs' Hill, now Montmartre).

Lutetia was renamed Paris in 212, taking its name from the Celtic Parisii.

Very little is now left of the ancient city. In a small park on high ground in the Latin Quarter of the Left Bank, tucked behind apartment blocks, one may still see some remains of the 1st century Arène de Lutèce. The only other signs of Roman Lutetia are the remains of public baths at the Musée de Cluny and the catacombs under Montparnasse.

There is also an asteroid named 21 Lutetia; and the element lutetium was named after the city, in honour of its discovery in a Paris laboratory.