Sonntag is a municipality in the district of Bludenz, in the Austrian state of Vorarlberg. It lies in the westernmost part of Austria, within a district whose administrative centre is the town of Bludenz.
As a municipality, Sonntag is one of the local administrative units that make up the Bludenz district, alongside the other communes of the surrounding area. The district itself belongs to Vorarlberg, the federal state that borders Germany to the north and Switzerland to the west.