The S12 is one of the network's lines connecting the cantons of Zürich, Aargau, Schaffhausen, Thurgau and St.

[4] At Zürich HB, trains of the S12 service usually depart from underground tracks (Gleis) 41–44 (Museumstrasse station).

The alternation of trains to Schaffhausen and Wil SG Seen provides an hourly service to each terminus.

[4][5][6] As of the December 2022 timetable change,[update] S12 services are operated by RABe 511 units, except for weekday services to Schaffhausen which are run by Re 450 class locomotives pushing or pulling double-deck passenger carriages.

The alternation of trains to Seuzach and Winterthur Seen provided an hourly service to each terminus.