Sihl Valley (German: Sihltal) is a river valley and belongs to the Zimmerberg-Sihltal region located in the district of Horgen in the Canton of Zurich , Switzerland. Commonly Sihltal is used as the name of the Lower Sihl Valley, i.e. the area in the southwest of the city of Zürich.

The area alongside Lake Zürich had been formed as the left moraine of the Ice Age glacier, the bed of which is now the Lake Zürich and the valley of the Sihl. Sihl valley is extensively wooded, but also cultivated and heavily populated in its lower parts. The Sihl (German pronunciation: [ˈsiːl]) is the name of a 68 km (42 mi) long river located in the cantons of Schwyz (SZ) and Zürich (ZH).