The Lužnice is a river in the Czech Republic and Austria, a right tributary of the Vltava River. It flows through Lower Austria and through the South Bohemian Region. It is 197.9 km (123.0 mi) long, of which 157.7 km (98.0 mi) is the Czech Republic, which makes it the 11th longest river in the Czech Republic.

The Vltava is the longest river in the Czech Republic, running southeast along the Bohemian Forest and then north across Bohemia, through Český Krumlov, České Budějovice and Prague, and finally merging with the Elbe at Mělník. It is commonly referred to as the "Czech national river".