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.

German reunification was the process of re-establishing Germany as a single full sovereign state, which took place between 9 November 1989 and 15 March 1991. The "Unification Treaty" entered into force on 3 October 1990, dissolving the German Democratic Republic and integrating its recently re-established constituent federated states into the Federal Republic of Germany to form present-day Germany. This date has been chosen as the customary German Unity Day, and has thereafter been celebrated each year as a national holiday in Germany since 1991. As part of the reunification, East and West Berlin were also de facto united into a single city, which eventually became the capital of Germany according to the Unification Treaty.