The Seetalbahn is a 1,435 mm (4 ft 8 1⁄2 in) (standard-gauge) railway of the Swiss Federal Railways between Lenzburg and Lucerne in Switzerland. The track, when created, was originally named the Swiss Lake Valley Railway Company and was owned by British investors. The passengers included tourists from Lucerne doing sightseeing tours to the Hallwilersee and Baldeggersee lakes. On September 3, 1883, the first section was opened. Expansions of the main line followed, as well as a short branch line between Beinwil and Beromünster. The branch line was closed down, however, in 1997.
Before it was purchased by the Swiss Confederation and integrated in the Swiss Federal Railways in 1922, the Seethalbahn (spelling of the period) even had restaurant carriages. It was a pioneer of the electrification of Switzerland's railways, starting electric service in 1910 with 5500 V 25 Hz a.c. In 1930 SBB normalized the electrification to 15 kV 162⁄3 Hz.
The Seetalbahn had the worst safety record of all Swiss Federal Railways lines, caused by many unguarded level crossings and the circumstances that it was originally constructed as a long distance tramway. In the villages between Lenzburg and Emmen it still runs beside roads and adjacent houses.