Lake Constance, also known as Bodensee, lake of central Europe, in the Alps, bordered by Switzerland, Germany, and Austria, about 400 m (1,310 ft) above sea level. After Lake Geneva it is the largest of the Alpine lakes, having a maximum length of about 74 km (46 mi) and a maximum breadth of about 16 km (10 mi). The area of the lake is about 539 sq km (208 sq mi), and the greatest depth, 252 m (827 ft). Lake Constance extends north-west and south-east. At the north-western end it is divided by a peninsula into two forks north of the city of Constance (Konstanz), Germany. The northern fork is called the Überlingersee and the southern fork is the Untersee. The main body of the lake is known as the Obersee. The lake is on the course of the Rhine, which enters from the south and then emerges from the Untersee in a westerly direction. A number of minor streams discharge into the lake, nearly all of them on the north-eastern side. The water of the lake is subject to sudden rises of up to 3.7 m (12 ft), partly because of the melting of the Alpine snows. The waters are clear, and the lake is rich in fish. The chief towns bordering the lake are Constance and Friedrichshafen, Germany; Rorschach, Switzerland; and Bregenz, Austria.

In prehistoric times the shallow areas of Lake Constance were the site of an extensive community of lake dwellers. Studies of the remains of the ancient lake dwellings have established Lake Constance as one of the most important sources of knowledge of this period of human history. Remains of a famous 8th-century Benedictine monastery on the island of Reichenau, with their monumental wall paintings and illuminations, were designated a UNESCO World Heritage Site in 2000.