Welthauptstadt Germania or World Capital Germania was the projected renewal of the German capital Berlin during the Nazi period, part of Adolf Hitler's vision for the future of Nazi Germany after the planned victory in World War II. It was to be the capital of his planned "Greater Germanic Reich". Albert Speer, the "first architect of the Third Reich", produced many of the plans for the rebuilt city in his capacity as overseer of the project, only a small portion of which was realised between the years 1938 and 1943.

Berlin is the capital and largest city of Germany, both by area and by population. Its more than 3.85 million inhabitants make it the European Union's most populous city, as measured by population within city limits. Simultaneously, the city is one of the states of Germany, and is the third smallest state in the country in terms of area. Berlin is surrounded by the state of Brandenburg, and Brandenburg's capital Potsdam is nearby. The urban area of Berlin has a population of over 4.5 million and is therefore the most populous urban area in Germany. The Berlin-Brandenburg capital region has around 6.2 million inhabitants and is Germany's second-largest metropolitan region after the Rhine-Ruhr region, and the fifth-biggest metropolitan region by GDP in the European Union.