Rapperswil (Swiss Standard German pronunciation: [ˈrapərsˌvɪl]; Swiss German pronunciation: [ˈrɑpːərʃˌʋiːl] or [ˈrɑpːərsˌʋiːl]; short: Rappi) is a former municipality and since January 2007 part of the municipality of Rapperswil-Jona in the Wahlkreis (constituency) of See-Gaster in the Canton of St. Gallen in Switzerland, located between Obersee and the main part of Lake Zurich.

Rapperswil is located on the northern shore of Lake Zurich at the point at which the lake is cut in two by the Seedamm isthmus, which is an ice age moraine. The upper (or eastern) part of Lake Zurich is called Obersee. Part of the old town, the castle and monastery are situated on a peninsula.

The town's main sights are concentrated in the Altstadt of Rapperswil and can be seen while strolling through the medieval alleys.