The Léman Express[3][4][5] is a commuter rail network for the transborder agglomeration of Grand Genève[6] (Greater Geneva) in west Switzerland and the French Alps (Haute-Savoie and Ain).

The Léman Express marked the start of direct services from Genève-Cornavin station to the French cities of Évian, Thonon, Annemasse and Annecy as well as the population of the Arve Valley up to Saint-Gervais-les-Bains.

The line was subsequently upgraded to the standard 25 kV AC electrification (as used on much of the French railways) in conjunction with the development of the Léman Express system.

The studies were necessitated by the growing number of commuters living in France and working in Geneva, not only on the short, existing RER system but on the lines leaving the station at Eaux Vives on the south side of the lake.

At the time of study, services carried some 7'000 commuters a day; with the improved network this was expected to grow to over 35'000 and cut up to 50'000 car journeys between France and Switzerland.

As part of the scheme and to avoid RER rolling stock needing three voltages, Cornavin – La Plaine – Bellegarde was re-electrified at 25 kV AC in summer 2014.

The French signalling and train control between Geneva and la Plaine was replaced with standard Swiss equipment, the points motors renewed and the line fully automated.

As the passing loops were finished before the CEVA tunnel, quarter hourly service to Coppet was started on 9 December 2018, over a year in advance of the full rollout of the Léman Express.

Local stations between Coppet and Allaman, the southern extent of the RER Vaud, were closed: Founex, Céligny, Crans, Prangins, Gilly-Bursinel and Perroy.

This line used to be electrified at 1500 V DC and signalled to SNCF standards from the border to both Geneva's central passenger station and La Praille goods depot.

On 20 February 2020, about three months after the full opening of the network, a steering committee composed of Swiss and French representatives met to revive the Tonkin Railway, a 17.8 km section between Saint-Gingolph and Évian-les-Bains.