The Jungfrau Railway is a mountain rack railway in the Bernese Alps, Switzerland, connecting Kleine Scheidegg in the Bernese Oberland to the Jungfraujoch, across the Valais border. It is the highest railway in Switzerland and Europe, running 9 kilometres (5.6 mi) from the station of Kleine Scheidegg to the Jungfraujoch, well above the perennial snow line. As a consequence, the railway runs essentially within the Jungfrau Tunnel, built into the neighbouring Eiger and Mönch, to protect the line from snow and extreme weather.

A rack railway is a steep grade railway with a toothed rack rail, usually between the running rails. The trains are fitted with one or more cog wheels or pinions that mesh with this rack rail. This allows the trains to operate on steep grades above 10%, which is the maximum for friction-based rail. Most rack railways are mountain railways, although a few are transit railways or tramways built to overcome a steep gradient in an urban environment.