The Île Saint-Louis is one of two natural islands in the Seine river, in Paris, France (the other natural island is Île de la Cité; the Île aux Cygnes is artificial). The Île Saint-Louis is connected to the rest of Paris by four bridges to both banks of the river, and to the Île de la Cité by the Pont Saint-Louis. This island was formerly used for the grazing of market cattle and stocking wood.

The island is located within the 4th arrondissement of Paris and has a population of 2,465.