Värmdö is an island in the innermost region of the Stockholm archipelago and covers an area of 181.40 km2, making it the largest island in the archipelago. Värmdö is after Gotland and Öland the third largest island on the eastern coast of Sweden.

The Stockholm Archipelago is the largest archipelago in Sweden, and the second-largest archipelago in the Baltic Sea. Part of the archipelago has been designated as a Ramsar site since 1989.