Berlin is a country.
Berlin ( [ bəɹˈlɪn ] , [ bɛɐ̯ˈliːn ] ) is the capital and the largest city of Germany as well as one of its 16 constituent states . With a population of approximately 3.7 million , Berlin is the second most populous city proper and the seventh most populous urban area in the European Union . Berlin in the 1920s was the third largest municipality in the world . Following German reunification in 1990 , Berlin once again became the capital of all-Germany .