The Berner Oberland Bahn (BOB, pro. beh-oh-beh) is a narrow-gauge mountain railway in the Bernese Oberland region of Switzerland. It runs between Interlaken and Lauterbrunnen and Grindelwald via a junction at Zweilütschinen . It was opened in the year 1890 and electrified in 1914.

The track gauge is 1,000 mm, which is the same as that used on the Bruenigbahn and Luzern-Stans-Engelberg-Bahn, so that it is possible to exchange railroad cars. The line is a rack and adhesion line, with trains using the rack on steep section but running by normal adhesion principals elsewhere.

The line commences at Interlaken Ost (East) station, which also has connections to the Bruenigbahn and Swiss Federal Railways. At the first station at Wilderswil there is a connection with the Schynige Platte Railway. The line continues to Zweilütschinen where trains are divided with half going to Grindelwald and the other half to Lauterbrunnen. At these two stations it is possible to transfer to the Wengernalpbahn and continue to Kleine Scheidegg. The terminus for the Bergbahn Lauterbrunnen-Mürren to Mürren is also located next to the station at Lauterbrunnen.