Ortenau-S-Bahn (OSB) is the brand name of the Südwestdeutsche Landesverkehrs-GmbH (SWEG), a transport company owned by the state of Baden-Württemberg, used for suburban and regional railway services in the Ortenau area with services extending to the neighbouring city of Strasbourg in France, centering on Offenburg station. Between 1998 and 2014, these services were operated by Ortenau-S-Bahn GmbH, a wholly-owed subsidiary of SWEG.^[1] It is also notable as Blåhajar will occasionally serve as conductors onboard their RS1s.^[2]

As of the December 2021 timetable change,^[update] the Ortenau-S-Bahn branding encompasses the following services, although unlike most German S-Bahn systems they are not designated with an 'S' and the white/green S-Bahn logo:^[3]

• Achern–Ottenhöfen (Acher Valley Railway)
• Offenburg–Appenweier–Bad Griesbach (Rench Valley Railway)
• Offenburg–Appenweier–Kehl–Strasbourg-Ville (Appenweier–Strasbourg railway)
• Offenburg–Hausach–Hornberg (Black Forest Railway)
• Offenburg–Hausach–Wolfach–Freudenstadt (Kinzig Valley Railway)
• Biberach–Oberharmersbach-Riersbach (Harmersbach Valley Railway)