The Bodensee–Toggenburg railway is a mainly single-track standard-gauge line connecting Romanshorn on Lake Constance and the Toggenburg region in Eastern Switzerland. It was built by the Bodensee-Toggenburg-Bahn (BT), a former railway company, which existed from 1910 until its merger with the "old" Südostbahn (SOB) to form the "new" Südostbahn (SOB) on 1 January 2001. Today, the line together with the Wattwil–Ebnat-Kappel section forms the eastern network of the Südostbahn.