Agde Cathedral (Cathédrale Saint-Étienne d'Agde) is a Roman Catholic cathedral dedicated to Saint Stephen located in Agde in the Hérault département of southern France. It stands on the bank of the Hérault River.

The present building was constructed in the 12th century, replacing a Carolingian church of the 9th century that stood on the foundations of a 5th century Roman church, formerly a temple of Diana.

It was formerly the seat of the Bishop of Agde. The see was not restored after the French Revolution and by the Concordat of 1801 its parishes were added to the Diocese of Montpellier.

The cathedral is remarkable for being constructed of black basalt from the nearby volcanic Mont St. Loup quarries.

The building is extremely strong and was designed to serve as a fortress as much as a church: the walls are between 2 and 3 metres thick, and the square tower, 35 metres high, could also function as a keep, or donjon.