Mattsee is a market town in the district of Salzburg-Umgebung, in the Austrian state of Salzburg. It lies at the lake of the same name, which shares the town's name.
As a market town (Marktgemeinde), Mattsee holds that status within Austria's municipal structure and belongs administratively to the Salzburg-Umgebung district, the district surrounding the city of Salzburg. Its position on the shore of the Mattsee lake is its defining geographic feature.