The former eastern territories of Germany refer in present-day Germany to those territories east of the current eastern border of Germany, i.e., the Oder–Neisse line, which historically had been considered German and which were annexed by Poland and the Soviet Union after World War II in Europe. In most of these territories, Germans used to be the dominant or sole ethnicity. In contrast to the lands awarded to the restored Polish state by the Treaty of Versailles after World War I, the German territories lost with the Potsdam Agreement after World War II in Europe on 2 August 1945 were either almost exclusively inhabited by Germans before 1945, mixed German-Polish with a German majority, or mixed German-Czech with a German majority (Glatz). Virtually the entire German population of the territories that did not flee voluntarily in the face of the Red Army advance of 1945, was violently expelled to Germany, with their possessions being seized and looted.

The Treaty on the Final Settlement with Respect to Germany , or the Two Plus Four Agreement , is an international agreement that allowed the reunification of Germany in October 1990. It was negotiated in 1990 between the 'two', the Federal Republic of Germany and the German Democratic Republic, in addition to the Four Powers which had occupied Germany at the end of World War II in Europe: France, the Soviet Union, the United Kingdom, and the United States. The treaty supplanted the 1945 Potsdam Agreement: in it, the Four Powers renounced all rights they had held with regard to Germany, allowing for its reunification as a fully sovereign state the following year. Additionally, the two German states agreed to reconfirm the existing border with Poland, accepting that German territory post-reunification would consist only of what was presently administered by West and East Germany—renouncing explicitly any possible claims to the former eastern territories of Germany including East Prussia, most of Silesia, as well as the eastern parts of Brandenburg and Pomerania.