It links the spa resort of St. Moritz, in the canton of Graubünden, Switzerland, with the town of Tirano, in the Province of Sondrio, Italy, via the Bernina Pass.

The elevation difference on the section between the Bernina Pass and Tirano is 1,824 m (5,984 ft), allowing passengers to view glaciers along the line.

The concession for the line was obtained in 1906, and the construction was financed by the investors in Kraftwerke Brusio AG, the builders of the hydro-electric works, without the aid of cantonal subsidy.

The RhB modernised the line fundamentally, also for military reasons, and completely renewed the section at the top of the pass.

Previously, the line formation on the north ramp of the Bernina Pass had been laid out in curves giving passengers extensive views, but also lying in the path of avalanche courses.

The new parts of the line cut off those curves, the catenary and the flat bottomed rails of the old formation were removed, but the substructure is still visible in the high mountains.

Since the mid-1980s, the Rhaetian Railway has been marketing the natural and technical attractions of the Bernina line specifically to tourists.

The Bernina line leaves St Moritz station in an easterly direction, and crosses the Inn River on a 64 m (210 ft) long viaduct.

The next station, Celerina Staz, is, at 1,716 m (5,630 ft) above sea level, the lowest point on the north side of the Bernina Pass.

After returning to the banks of the Inn, the line reaches the small station Punt Muragl Staz.

On track 3 is also the exchange of locomotives for the famous Bernina Express, which operates between Chur or Davos Platz and Tirano.

Past the other end of the station is the world-famous Montebello Curve, where the line meets the road over the pass.

The railway now runs along the eastern bank of the lake, and, near Ospizio Bernina, reaches its highest point, at 2,253 m (7,392 ft) above sea level.

After the stopping point Li Curt, erected only in 1977, the line ends up running on a street in the village of Le Prese.

Still in service also six ABe 4/4III and two Gem 4/4 that can operate without electrical feeding, thanks their diesel-generator inside (double engine locomotives).

Despite being set up originally only for tourist traffic, the Bernina line now also assists trade with Italy by carrying considerable quantities of freight, consisting mostly of heating oil, fuels and timber.

The flagship services are the now fully panorama car-equipped Bernina Express and the Trenino Rosso travelling in the opposite direction.

In connection with the danger of avalanches on the Bernina line, the Rhaetian Railway has developed an unusual procedure for the removal of these high alpine hazards.