Together with the Simplon Tunnel south of Brig, it constitutes one of the major railways through the Alps and an important north-south axis in Europe.

Its culminating point is 1,240 metres (4,070 ft) above sea level, making it the highest adhesion and standard gauge railway in Switzerland.

The more recent Lötschberg Base Tunnel replaces most of the open-air section of the mountain line and allows faster travel between Bern and Brig.

From there the line runs generally due south through the Kander valley, passing through Mülenen, Reichenbach and Frutigen, where the north portal of the Base Tunnel is located.

The line passes through another tunnel before it turns in an easterly direction to the southern flank of the Bietschhorn just before reaching Hohtenn Station, 450 metres (1,480 ft) above the Rhone.

The line then continues eastward, descending towards Brig, crossing the wild valleys of Jolital, Bietschtal, Baltschiedertal and Gredetschtal, and passing through Ausserberg, Eggerberg and Lalden.

The line, especially its southern part, lies in close proximity to the Jungfrau-Aletsch area, a largely glaciated region between the Lötschen and Grimsel passes.

In 1891 a small group of eminent persons obtained a concession for the construction of a railway line between Spiez and Frutigen with the option of later extending it into the Valais.

On 27 July 1906, the Berner Alpenbahngesellschaft Bern-Lötschberg-Simplon (BLS) was founded for the construction and operation of the proposed railway and on 1 January 1907, it absorbed the Spiez-Frutigen-Bahn.

On 24 July 1908 a collapse of weak strata caused a sudden flood in the Lötschberg tunnel killing 25 people, all but three of the workers on the shift.

The rolling stock for the construction lines consisted of 420 waggons and 32 small steam locomotives with Klien-Lindner axles, delivered from June to November 1907 by the German firm of Orenstein & Koppel.

The engineer J. Seeberger was responsible for building a construction railway between Frutigen and the tunnel portal near Kandersteg; it was over 15 km (9.3 mi) long and climbed about 429 m (1,407 ft) in altitude.

The earthworks and structures of the construction railway were completed on 30 June 1907 and on 19 August the first steam locomotive ran to the portal of the tunnel.

The building of the construction railway on the south side was delayed by many appeals and the groundbreaking ceremony near Naters took place on 12 February 1907.

At the same time the tracks were lowered to create a continuous SIM corridor (Simplon Inter-Modal) for a rolling highway (trucks carried on flatcars) and high-cube containers.

In addition, the car ferry continues to operate between Kandersteg and Goppenstein; it is subsidized by the Swiss government to substitute for a road tunnel under the Rawil Pass that was planned in the 1970s but never built.