Lake Constance refers to three bodies of water on the Rhine at the northern foot of the Alps: Upper Lake Constance, Lower Lake Constance, and a connecting stretch of the Rhine, called the Lake Rhine. These waterbodies lie within the Lake Constance Basin, which is part of the Alpine Foreland and through which the Rhine flows.
The lake is situated where Germany, Switzerland, and Austria meet. Its shorelines lie in the German states of Baden-Württemberg and Bavaria, the Swiss cantons of St. Gallen, Thurgau, and Schaffhausen, and the Austrian state of Vorarlberg. The Rhine flows, as Alpine Rhine, into the lake from the south, with its original course forming the Austro-Swiss border, and has its outflow on the Lower Lake where — except for Schaffhausen — it forms, as High Rhine, the German-Swiss border as far as the city of Basel.
The most populous towns on the Upper Lake are Constance, Friedrichshafen, Bregenz, Lindau, Überlingen and Kreuzlingen. The largest town on the Lower Lake is Radolfzell am Bodensee. The largest islands are Reichenau in the Lower Lake, and Lindau and Mainau in the Upper Lake.