The Tösstalbahn opened between Winterthur Grüze and Bauma was on 4 May 1875, and its continuation to Wald opened on 15 October 1876. At Wald the line connected with the independently owned Wald-Rüti-Bahn from Rüti ZH, which had itself opened on 29 September 1876. The two lines remained in separate ownership until they both became part of the Swiss Federal Railways on 10 June 1918, although the TTB had operated the WB from 1902. In 1901, the Uerikon-Bauma-Bahn opened, providing a third access point to the Tösstal line at Bauma. This line was never a great success, and in 1948 much of it was abandoned, but the stretch from Hinwil to Bauma was acquired by the SBB, retained and electrified. However passenger services ceased by 1979, and the Hinwil to Bauma section is now operated as a preserved railway by the Dampfbahn-Verein Zürcher Oberland. In 1990, the passenger service on the Tösstalbahn became part of the Zürich S-Bahn network. Operation remained the responsibility of the SBB, with service provided using RBDe 560, with occasional RBe 540 supplements. Einheitswagen I or II as well as a BDt or Bt control car made up the rest of the consist, all of which were generally in the NPZ livery. In December 2006, THURBO, a regional railway partly owned by the SBB, took over the operation of the S26 passenger service and provided new rolling stock. The line remains in the ownership of the SBB. Since December 2018, the S 11 Aarau - Lenzburg - Dietikon - Zurich HB - Stettbach - Winterthur - Seuzach/Sennhof-Kyburg has been operating on a section of the Tösstalbahn. During rush hours, the upgrades that have taken effect enable the S-Bahn to run an hourly service to Wila, but without stopping in Rämismühle-Zell. In 2019, the continuous half-hourly interval of the S26 between Winterthur and Rüti ZH has been introduced.
The S26 provides the only regular passenger service over the bulk of the Tösstalbahn. It provides an hourly service between Winterthur and Rüti, with additional trains giving two trains per hour on the section between Winterthur and Bauma. A journey along the full route takes 64 minutes. The stations in the Winterthur suburbs are also served by other S-Bahn services, with the S12 serving Winterthur Seen and Winterthur Grüze stations, and the S35 serving Winterthur Grüze only.
Rolling stock
Passenger service is in the hands of Stadler GTW units provided by THURBO.