From the Wikipedia page 
Svalbard lies under the sovereignty of Norway, but the Svalbard Treaty places several restrictions. Norway cannot use the archipelago for warlike purposes, cannot discriminate economic activity based on nationality and is required to conserve the natural environment. Uniquely, Svalbard is entirely visa-free zone. Everybody may live and work in Svalbard indefinitely regardless of country of citizenship. Svalbard Treaty grants treaty nationals equal right of abode as Norwegian nationals. Non-treaty nationals may live and work indefinitely visa-free as well. "Regulations concerning rejection and expulsion from Svalbard" is in force on non-discriminatory basis.
Public administration of the archipelago is the responsibility of the Governor of Svalbard, who acts as county governor and chief of police. The institution was established by and is regulated by the Svalbard Act, which also limits which Norwegian laws apply to the islands. Longyearbyen Community Council is the only elected local government and is organized similar to a mainland municipality. Other Norwegian government agencies with a presence are the Directorate of Mining and the Tax Administration. The only diplomatic mission is the Consulate of Russia in Barentsburg.
The archipelago was spotted in 1596, and soon companies from England, the Netherlands, Denmark–Norway and France were whaling and hunting. Both England and Denmark–Norway claimed the land, while the Dutch and France claimed the mare liberum principle, resulting in Svalbard becoming terra nullius—land without sovereignty. Work on establishing a public administration started in the 1870s, but did not progress until the 1900s, when the establishment of coal mining communities created a more urgent need. The Svalbard Treaty was signed following the Paris Peace Conference in 1920, and the governor and act came into effect in 1925. By then only Norwegian and Russian communities remained.
After the Second World War and the outbreak of the Cold War, Svalbard became polarized with Norwegian and Soviet communities isolated from each other. Norway carried out a more defensive foreign policy on Svalbard compared to on the mainland, and foreign activity was held at a minimum. The Soviet Union issued protests against virtually all new Norwegian activity. At the time there were twice as many Soviet citizens as Norwegians on the islands. More than half the archipelago was conserved in 1973. Since the 1990s Longyearbyen has become "normalized", abandoned the company town structure and seen its population doubled. On the other hand, the Soviet communities have dwindled, with only a few hundred residents remaining in Barentsburg.