The Ortenau S-Bahn (OSB) is a regional railway operator in the German state of Baden-Württemberg. It is a subsidiary of the Südwestdeutsche Verkehrs-Aktiengesellschaft (SWEG), a transport company owned by the state of Baden-Württemberg.
The Ortenau S-Bahn operates services over DB Netz AG owned tracks in the area around Offenburg. Services connect Offenburg to Appenweier, Kork, Kehl, Strasbourg, Bad Greisbach, Hausach and Freudenstadt. They run over sections of the Rhine Valley, Black Forest and Appenweier–Strasbourg main lines, together with the Renchtalbahn and Kinzigtalbahn branch lines.