Copenhagen[a] (Danish: København [kʰøpm̩ˈhɑwˀn] (About this soundlisten)) is the capital and most populous city of Denmark. As of 1 January 2020, the city had a population of 794,128 with 632,340 in Copenhagen Municipality, 104,305 in Frederiksberg Municipality, 42,989 in Tårnby Municipality, and 14,494 in Dragør Municipality.[3][7][8] It forms the core of the wider urban area of Copenhagen (population 1,330,993) and the Copenhagen metropolitan area (population 2,057,142). Copenhagen is situated on the eastern coast of the island of Zealand; another portion of the city is located on Amager, and it is separated from Malmö, Sweden, by the strait of Øresund. The Øresund Bridge connects the two cities by rail and road.

Originally a Viking fishing village established in the 10th century in the vicinity of what is now Gammel Strand, Copenhagen became the capital of Denmark in the early 15th century. Beginning in the 17th century, it consolidated its position as a regional centre of power with its institutions, defences, and armed forces. During the Renaissance the city served as the de facto capital being the seat of government of the Kalmar Union, governing the entire present day Nordic region in a personal union with Sweden and Norway ruled by the Danish monarch serving as the head of state. The city flourished as the cultural and economic center of Scandinavia under the union for well over 120 years, starting in the 15th century up until the beginning of the 16th century when the union was dissolved with Sweden leaving the union through a rebellion. After a plague outbreak and fire in the 18th century, the city underwent a period of redevelopment. This included construction of the prestigious district of Frederiksstaden and founding of such cultural institutions as the Royal Theatre and the Royal Academy of Fine Arts. After further disasters in the early 19th century when Horatio Nelson attacked the Dano-Norwegian fleet and bombarded the city, rebuilding during the Danish Golden Age brought a Neoclassical look to Copenhagen's architecture. Later, following the Second World War, the Finger Plan fostered the development of housing and businesses along the five urban railway routes stretching out from the city centre.

Since the turn of the 21st century, Copenhagen has seen strong urban and cultural development, facilitated by investment in its institutions and infrastructure. The city is the cultural, economic and governmental centre of Denmark; it is one of the major financial centres of Northern Europe with the Copenhagen Stock Exchange. Copenhagen's economy has seen rapid developments in the service sector, especially through initiatives in information technology, pharmaceuticals and clean technology. Since the completion of the Øresund Bridge, Copenhagen has become increasingly integrated with the Swedish province of Scania and its largest city, Malmö, forming the Øresund Region. With a number of bridges connecting the various districts, the cityscape is characterised by parks, promenades, and waterfronts. Copenhagen's landmarks such as Tivoli Gardens, The Little Mermaid statue, the Amalienborg and Christiansborg palaces, Rosenborg Castle Gardens, Frederik's Church, and many museums, restaurants and nightclubs are significant tourist attractions.

Copenhagen is home to the University of Copenhagen, the Technical University of Denmark, Copenhagen Business School and the IT University of Copenhagen. The University of Copenhagen, founded in 1479, is the oldest university in Denmark. Copenhagen is home to the F.C. Copenhagen. The annual Copenhagen Marathon was established in 1980. Copenhagen is one of the most bicycle-friendly cities in the world.

The Copenhagen Metro, launched in 2002, serves central Copenhagen. Additionally, the Copenhagen S-train, the Lokaltog (private railway), and the Coast Line network serve and connect central Copenhagen to outlying boroughs. Serving roughly two million passengers a month, Copenhagen Airport, Kastrup, is the busiest airport in the Nordic countries.