The Cathedral Basilica of Saint Denis (French: Cathédrale royale de Saint-Denis, or simply Basilique Saint-Denis, previously the Abbaye de Saint-Denis) is a large medieval abbey church in the commune of Saint-Denis, now a northern suburb of Paris. The abbey church was created a cathedral in 1966 and is the seat of the Bishop of Saint-Denis, Pascal Michel Ghislain Delannoy. The building is of unique importance historically and architecturally.

Founded in the 7th century by Dagobert I on the burial place of Saint Denis, a patron saint of France, the church became a place of pilgrimage and the burial place of the French Kings, nearly every king from the 10th to the 18th centuries being buried there, as well as many from the previous centuries. (It was not used for the coronations of kings, this role being designated to the Cathedral of Reims; however, queens were commonly crowned there.) "Saint-Denis" soon became the abbey church of a growing monastic complex. In the 12th century the Abbot Suger rebuilt portions of the abbey church using innovative structural and decorative features that were drawn from a number of other sources. In doing so, he is said to have created the first truly Gothic building. The basilica's 13th century nave is also the prototype for the Rayonnant Gothic style, and provided an architectural model for cathedrals and abbeys of northern France, England and other countries.