Oslo is the capital and largest city in Norway. Founded around 1048 by King Harald III "Hardrada" of Norway, the city was largely destroyed by a fire in 1624. The Danish–Norwegian king Christian IV rebuilt the city as Christiania (briefly also spelt Kristiania). In 1925 the city reclaimed its original Norwegian name, Oslo. The diocese of Oslo is one of the five original dioceses in Norway, which originated around the year 1070.

Oslo is the cultural, scientific, economic and governmental centre of Norway. The city is also a hub of Norwegian trade, banking, industry and shipping. It is also an important centre for maritime industries and maritime trade in Europe. The city is home to many companies within the maritime sector, some of them are amongst the world's largest shipping companies, shipbrokers and maritime insurance brokers.

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. For several years, Oslo has been listed as one of the most expensive cities in the world along with such other global capitals as Copenhagen, Paris, and Tokyo. In 2009, however, Oslo regained its status as the world's most expensive city. Oslo is a pilot city of the Council of Europe and the European Commission intercultural cities programme.

As of 2010, the metropolitan area of Oslo has a population of 1,422,442 of whom 907,288 lives in the contiguous conurbation. The population currently increases at a record rate of over 2% annually, making it the fastest growing capital in Europe. A large portion of this growth stems from immigration increasingly changing Oslo into a cosmopolitan city. The immigrant share of the population in the city proper now counts more than 25%.