The Aare is the longest river that flows entirely within Switzerland. Its total length is 288 km, the gradient is 1665 m, its catchment area is 17,709 km² and the average discharge is 560 m³/s. The Aare is the most water-rich tributary of the Rhine, even ahead of the Meuse, and it carries more water than the Moselle and Main combined.
The Aare rises in the two Aar glaciers in the eastern Bernese Alps on the Finsteraarhorn, west of the Grimsel Pass in central southern Switzerland. Its course leads through the cantons of Bern, Solothurn and Aargau. First it passes through the Aare Gorge, cut into a high rock ridge, and then reaches the plain between Meiringen and the glacial Lake Brienz. Shortly before entering Lake Thun near Interlaken, it is canalized and leaves this to the northwest into the wide Aare Valley. In the area of Bern, it flows around the medieval city center and reaches Lake Wohlen in a westerly direction. At Aarberg, it is channeled into Lake Biel via the Hagneck Canal and, after leaving the canal, follows the course of the Jura Mountains northeastward. Below Brugg, it receives the Reuss and the Limmat before flowing into the Rhine near Koblenz (CH).
In the course of its geological development, the Aare was successively the upper course of the Danube, the Rhone and the Rhine.