The Lötschberg Base Tunnel (LBT) is a 34.57 km (21.48 mi) railway base tunnel on the BLS AG's Lötschberg line cutting through the Bernese Alps of Switzerland some 400 m (1,300 ft) below the existing Lötschberg Tunnel. It runs between Frutigen, Bern, and Raron, Valais.

BLS AG is a Swiss railway company created by the 2006 merger of BLS Lötschbergbahn and Regionalverkehr Mittelland AG. 55.8% of it is owned by the canton of Berne, and 21.7% by the Swiss Confederation. It has two main business fields: passenger traffic and infrastructure.