German Unity Day is the National Day of Germany, celebrated on 3 October as a public holiday. It commemorates German reunification in 1990 when the German Democratic Republic (East Germany) ceased to exist and joined the Federal Republic of Germany (West Germany), so that for the first time since 1945 there existed a single German state. German Unity Day on 3 October has been the German national holiday since 1990, when the reunification was formally completed.
An alternative choice to commemorate the reunification could have been the day the Berlin Wall came down: 9 November 1989, which coincided with the anniversary of the proclamation of the German Republic in 1918, and the defeat of Hitler's first coup in 1923.