The Gotthard Tunnel (German: Gotthardtunnel, Italian: Galleria del San Gottardo) is a 15-kilometre-long (9.3 mi) railway tunnel that forms the summit of the Gotthard Railway in Switzerland. It connects Göschenen with Airolo and was the first tunnel through the Saint-Gotthard Massif in order to bypass the St Gotthard Pass. It was built as single bore tunnel accommodating a standard gauge double-track railway throughout. When opened in 1882, the Gotthard Tunnel was the longest tunnel in the world.

The tunnel rises from the northern portal at Göschenen (1,106 m or 3,629 ft) and the highest point (1,151 m or 3,776 ft) is reached after approximately eight kilometres (5 mi). After two more kilometers, the border between the cantons of Uri and Ticino is passed; after another five kilometres (3 mi), the tunnel ends at the southern portal near to Airolo (1,142 m or 3,747 ft).