Mainau is an island in Lake Constance (on the south shore of the Überlinger See near the city of Konstanz, Baden-Württemberg, Germany). It is maintained as a garden island and a model of excellent environmental practices. Administratively, the island has been a part of Konstanz since December 1, 1971, when the municipality of Litzelstetten, of which Mainau was part, was incorporated into Konstanz. Mainau is still part of Litzelstetten, now one of 15 wards of Konstanz.
The island belongs to the Lennart Bernadotte-Stiftung, an entity created by Prince Lennart, Count Bernadotte af Wisborg, formerly a Prince of Sweden and Duke of Småland. It is one of the main tourist attractions of Lake Constance. Beside flowers there is a park landscape with views on the lake. There is also a greenhouse with tropical climate and thousands of butterflies.