The St. Gallen S-Bahn (German: S-Bahn St. Gallen) is an S-Bahn-style commuter rail in Eastern Switzerland and neighbouring areas. The network connects stations in the Swiss cantons of Appenzell Ausserrhoden, Appenzell Innerrhoden, Glarus, Grisons, Schaffhausen, St. Gallen, Thurgau and Zurich, as well as a few stations in Austria (Bregenz, Vorarlberg) and Germany (Konstanz, Baden-Württemberg and Lindau, Bavaria). Some services also operate as part of the Bodensee S-Bahn.
Services are operated by Appenzeller Bahnen (AB), Südostbahn (SOB), and Thurbo. Within Switzerland and until Konstanz, services operate within the Tarifverbund Ostwind (Ostwind fare network) of northeastern Switzerland and Liechtenstein.