The network connects stations in the Swiss cantons of Appenzell Ausserrhoden, Appenzell Innerrhoden, Glarus, Grisons, Schaffhausen, St. Gallen, Thurgau and Zürich, as well as a few stations in Austria (Bregenz, Vorarlberg) and Germany (Konstanz, Baden-Württemberg and Lindau, Bavaria).

[1] Services are operated by Appenzeller Bahnen (AB), Südostbahn (SOB), and THURBO.

[2] As of December 2023[update], the network consists of 22 lines, numbered 1‒2, 4‒7, 9‒10, 12, 14‒15, 17, 20‒26, 44 and 81‒82, using the "S" prefix typical for most S-Bahn systems.

Unless stated otherwise, the lines are 1,435 mm or 4 ft 8+1⁄2 in standard gauge adhesion railways.

As of the December 2023 timetable change,[update] the following night routes existed:[8]