Rapperswil (rä´pərsvēl), town, St. Gall canton, NE Switzerland, on the Lake of Zürich. It has some diversified light industry. Allied with several Swiss cantons after the 15th cent., Rapperswil was included in St. Gall canton in 1803. It has a 14th-century castle, a 15th-century town hall, and a 17th-century Capuchin monastery. The town is the headquarters of the International Institute of Historic Castles.