Oslo is a county and municipality, as well as the capital and largest city in Norway. Founded around 1048 by King Harald III of Norway, the city was largely destroyed by a fire in 1624. The Danish–Norwegian king Christian IV moved and rebuilt the city closer to Akershus fortress and called it Christiania. In 1925 the city reclaimed its original Norwegian name, Oslo.

As of 2010, the metropolitan area of Oslo has a population of 1,422,442, which is currently increasing due to immigration at a record rate of over 2% annually, making it the fastest growing capital in Europe and a multicultural city. The immigrant share of the population in the city proper now counts more than 25%.

Oslo is the cultural, scientific, economic and governmental centre of Norway. It is an important centre for maritime industries and maritime trade in Europe. Oslo is considered a global city and ranked "Beta World City" in studies performed by the Globalization and World Cities Study Group and Network in 2008. In 2009, Oslo was ranked the world's most expensive city.