Lake Constance (German: Bodensee) is a lake on the Rhine at the northern foot of the Alps, and consists of three bodies of water: the Obersee ("upper lake"), the Untersee ("lower lake"), and a connecting stretch of the Rhine, called the Seerhein.

The lake is situated in Germany, Switzerland and Austria near the Alps. Its shorelines lie in the German states of Bavaria and Baden-Württemberg, the Austrian state of Vorarlberg, and the Swiss cantons of Thurgau, St Gallen and Schaffhausen. The river Rhine flows into the lake from the south, with its original course forming the Austro-Swiss border, and has its outflow of the "Lower Lake" where - except for Schaffhausen - it forms the German-Swiss border until the city Basel.