The Treaty of Saint-Germain-en-Laye was signed on 10 September 1919 by the victorious Allies of World War I on the one hand and by the Republic of German-Austria on the other. Like the Treaty of Trianon with Hungary and the Treaty of Versailles with the Weimar Republic, it contained the Covenant of the League of Nations and as a result was not ratified by the United States but was followed by the US–Austrian Peace Treaty of 1921.

The Republic of German-Austria was an unrecognised state that was created following World War I as an initial rump state for areas with a predominantly German-speaking and ethnic German population within what had been the Austro-Hungarian Empire, with plans for eventual unification with Germany. The territories covered an area of 118,311 km2 (45,680 sq mi), with 10.4 million inhabitants.