Seliger (Russian: Селиге́р, IPA: [sʲɪlʲɪˈgʲer]) is a lake in Ostashkovsky District of Tver Oblast and, in the extreme northern part, in Demyansky District of Novgorod Oblast of Russia, in the northwest of the Valdai Hills, a part of the Volga basin.

Valdaysky National Park covers the northern part of the lake.

Every year, Seliger camp forums bring together young people to study and discuss issues in political science, economics, art, literature and culture.

Ostashkov is the only town on the lake and is one of the most popular resorts in central Russia.

The closed urban-type settlement of Solnechny which is a military base occupies Gorodomlya Island.