The Great St Bernard Tunnel (French: Tunnel du Grand Saint-Bernard, Italian: Traforo del Gran San Bernardo, German: Grosser-Sankt-Bernhard-Tunnel) is a road tunnel complementing the Great St Bernard Pass, linking Martigny (in the Swiss canton of Valais) with Saint-Rhémy-en-Bosses (in the Aosta Valley, in north western Italy).

There is a toll to use the tunnel, payable in full even for drivers who already display on their vehicles a Swiss motorway vignette. The tunnel comprises a section of the E27 route linking Belfort with Aosta.

For most of its 5,798-metre (6,341 yd) length the tunnel runs in a straight line, but incorporates a gentle slope. The northern end is 1,918 m (6,293 ft) above sea level while the southern end is only 1,875 m (6,152 ft) above sea level. At both ends, the approach road to the tunnel is covered by a gallery/avalanche shelter in order to minimize the risk of access to the tunnel being temporarily blocked during bad weather.