Lake Zurich (German: Zürichsee, Swiss Standard German pronunciation: [ˈtsyːrɪçˌzeː]; Alemannic German: Zürisee) is a lake in Switzerland, that extends southeast of the city of Zurich. Depending on the context, Lake Zurich or Zürichsee may refer to the entire lake or specifically to the section downstream of the Hurden peninsula and Seedamm causeway (between Pfäffikon and Rapperswil). In the latter case, the upstream part of the lake is called Obersee (lit. 'Upper Lake'), while the lower part is sometimes also referred to as the Lower Lake (unterer Zürichsee), respectively.

Lake Zurich is a glacial lake that was formed by the Rhine-Linth glacier [de]. Its main tributary is the River Linth, which rises in the glaciers of the Glarus Alps. The Linth originally flowed directly into Lake Zurich, but was later diverted by the Escher canal (completed in 1811) into Lake Walen (Walensee) from where its waters are now carried to the east end of Lake Zurich (near Schmerikon) via the straightened Linth Canal (completed in 1816). Until the early 16th century, there was another lake upstream of Obersee, Lake Tuggen (Tuggenersee) near Tuggen. Water exits Lake Zurich at its northwestern end (at the level of the Quaibrücke), passing through the city of Zurich. However, this outflow is known as the Limmat. The Limmat is a tributary of the Aare, which itself is a tributary of the High Rhine. The highest point in the lake's drainage basin is the Tödi, at 3,614 metres (11,857 ft) above sea level.

In addition to the River Linth, other tributaries include the Jona, Schmerikoner Aa, Steinenbach, and Wägitaler Aa, which all flow into the Obersee, along with several creeks. The Seedamm, an artificial causeway and bridge, crosses the narrowest point of the lake at the level of the Hurden Peninsula, carrying a railway line and road from Rapperswil to Pfäffikon. The waterway is also crossed by the Holzbrücke Rapperswil-Hurden, a wooden pedestrian bridge. The eastern section of the lake is known as the Obersee (lit. 'Upper Lake'). West of the Seedamm lie the small islands of Lützelau and Ufenau, where in 1523 Ulrich von Hutten took refuge and died. Other islands include Grosser Hafner, Saffa Island and Schönenwerd (near Richterswil). A popular tourist destination is the Au peninsula at the village of Au between Wädenswil and Horgen. The lake shores are well cultivated and fertile. These include nature reserves such as Frauenwinkel and Bätzimatt. The bay of Rapperswil and reed in Nuolen are wintering areas for birds and popular sites for bird watching.

To the east, separated by Zürichberg-Adlisberg, Forch, and Pfannenstiel, are two smaller lakes, Greifensee (lit. 'Lake Greifen') and Pfäffikersee (lit. 'Lake Pfäffikon'). There are several minor lakes and ponds in the vicinity, such as Egelsee, Lützelsee or Türlersee. Zimmerberg, Etzel and Buechberg mountains lie to the west and south of the lake, respectively. Further to the east, the Speer, Chüemettler and Federispitz can be seen from the southern part of the lake.

Administratively, Lake Zurich is split between the cantons of Zurich (Horgen District), St. Gallen (See-Gaster) and Schwyz (Höfe and March districts). The lower lake, to the west of the Seedamm, is largely in the canton of Zurich, while the upper lake is shared between the cantons of St. Gallen and Schwyz.

The following rivers or streams flow into lower part of Lake Zurich. From the Limmat clockwise, they are:

Zurich, at the north-western end of the lake, is the largest city on Lake Zurich. The least populous is Hurden.

On the west shore (which gradually becomes the south shore) are Kilchberg, Rüschlikon, Thalwil, Oberrieden, Horgen, Au, Wädenswil and Richterswil in the canton of Zurich, and Freienbach, Pfäffikon, Hurden, Altendorf, Lachen, Nuolen and Tuggen in the canton of Schwyz.