The Basilica of Saint-Denis is a large former medieval abbey church and present cathedral in the city of Saint-Denis, a northern suburb of Paris. The building is of singular importance historically and architecturally as its choir, completed in 1144, is widely considered the first structure to employ all of the elements of Gothic architecture.

The basilica became a place of pilgrimage and a necropolis containing the tombs of the French Kings, including nearly every king from the 10th century through Louis XVIII in the 19th century. Henry IV of France came to Saint-Denis to formally renounce his Protestant faith and become a Catholic. The Queens of France were crowned at Saint-Denis, and the royal regalia, including the sword used for crowning the kings and the royal scepter, were kept at Saint-Denis between coronations.

The site originated as a Gallo-Roman cemetery in late Roman times. The archaeological remains still lie beneath the cathedral; the people buried there seem to have had a faith that was a mix of Christian and pre-Christian beliefs and practices. Around 475 St. Genevieve purchased some land and built Saint-Denys de la Chapelle. In 636 on the orders of Dagobert I the relics of Saint-Denis, a patron saint of France, were reinterred in the basilica. The relics of St-Denis, which had been transferred to the parish church of the town in 1795, were brought back again to the abbey in 1819.

In the 12th century, Abbot Suger rebuilt portions of the abbey church using innovative structural and decorative features. In doing so, he is said to have created the first truly Gothic building. In the following century the master-builder Pierre de Montreuil rebuilt the nave and the transepts in the new Rayonnant Gothic style.

The abbey church became a cathedral in 1966 and is the seat of the Bishop of Saint-Denis, Pascal Michel Ghislain Delannoy. Although known as the "Basilica of St Denis", the cathedral has not been granted the title of Minor Basilica by the Vatican.