The Váh (Slovak pronunciation: [ʋaːx]; German: Waag, pronounced [vaːk] ⓘ;[1] Hungarian: Vág;[2][3] Polish: Wag[4]) is the longest river within Slovakia.

Towns on the river include Liptovský Hrádok, Liptovský Mikuláš, Ružomberok, Vrútky, Žilina, Bytča, Považská Bystrica, Púchov, Ilava, Dubnica nad Váhom, Nemšová, Trenčín, Nové Mesto nad Váhom, Piešťany, Hlohovec, Sereď, Šaľa, Kolárovo and Komárno.

It could be derived from old Germanic wȃg (stream) or proto-Slavic vagъ, vaga (pole, stick, carved branch) referring to reinforced riverbanks.

The left tributaries are Demänovka, Revúca, Ľubochnianka, Turiec, Rajčanka and Nitra rivers, and the right tributaries are Belá, Orava, Varínka, Kysuca, Biela voda, Vlára, Dubová, Dudváh and Malý Dunaj rivers.

It includes canals, artificial dams (Čierny Váh, Liptovská Mara, Bešeňová, Krpeľany, Žilina, Hričov, Nosice, Sĺňava, Madunice, Kráľová and Selice) and 16 hydropower stations, whose construction started in the 1930s and increased after World War II.