Saint-Denis (créole: Sin-Dni) is the capital of Réunion Island and the city with the most inhabitants on the island. It hosts all the important administrative offices and is also a cultural center with numerous museums. Saint-Denis is also the largest city in all of the French Overseas Departments.

Saint-Denis is the prefecture (administrative seat) of the French island of Réunion. The island lies between Mauritius and Madagascar and has the status of a French Overseas Department and is officially an administrative division of France. The General Council and Regional Council, the Chamber of Commerce and Industry, the Chamber of Trades and Craft Industry, the rectorate, the state university, the employment office, and the customs authority are all located in the commune of Saint-Denis.
Saint-Denis was named in 1669 by Étienne Régnault, who later became governor of Réunion from 1665 to 1671. The settlement was named after the ship "Saint-Denis", which in 1664, as part of a fleet sailing under the flag of the French India Company, was sent to Réunion Island and then on to India. The aforementioned Governor Régnault arrived with the fleet from France and established a resupply outpost on the coast at Saint-Paul, the first capital of the island.
The small 60-ton ship "Saint-Denis", previously separated from the fleet at Tenerife in the Canary Islands, still managed to find its own way to the island, arriving in 1667. The captain of the ship, named Chanlette, was a good friend of Régnault, so the bay, the harbor, and later the city, were all subsequently named "Saint-Denis" in honor of the return of the lost ship. The ship was, in turn, named after Saint-Denis, a third-century bishop and missionary to Gaul, who was martyred with his companions Rusticus and Elentère in what would become modern-day France.
Under Mahé de Labourdonnais, then Governor of the East India Company and an important figure in the history of the island, the town of Saint-Denis replaced the former capital of Saint-Paul due to the general quality and favorable location of its harbor. Though the small settlement had just 2166 inhabitants, it had become the capital of the island and seat of the colonial government of the whole of the Mascarene islands.
In the year 1743, the first church and the new governor's palace (the modern Prefecture) were built. In 1771, a formal plan for the city was instituted. This followed the typical colonial grid pattern, with 12 streets in the east-west direction and 7 running north-south.
The administrative headquarters and warehouse of the French East India Company were established in 1773. It was built in the typical French colonial vernacular style and was later the official residence of the Governor and Prefect. In 1790, Saint-Denis was formally incorporated as a commune, and Jean Baptiste Delestrac became its first mayor.
Saint-Denis still remained only a small town, trailing behind Saint-Paul in population and Saint-Pierre in economic power. At the turn of the 19th century, the city was little more than a boring bureaucratic backwater, where the most exciting activity was still taking a walk. By mid-century, however, sugar barons had begun pouring money into the local economy, and Saint-Denis blossomed into an important cultural and commercial center. In 1852, both the colonial bank and the natural history museum were founded in the city.
By the 20th century, political and economic life on the island had become directly tied to the fortunes of the capital: Two world wars, malaria epidemics, and increasing cultivation of the sugar beet in Europe all lead to an economic recession in the city and on the island in general, from which it has only recently emerged, thanks to the establishment of subsidies from Paris and the European Union.
The primary ethnic groups of the city are European immigrants, former slaves, Chinese and Muslim Indian immigrants and their descendants, and créoles. The demographics are highly mixed, and ghettos of any particular ethnicity do not exist.