Vadsø (ˈvɑ̂dsøː; Čáhcesuolu; Vesisaari) is a municipality in Troms og Finnmark County, Norway. The administrative centre of the municipality is the town of Vadsø, which was the administrative centre of the former Finnmark county. Other settlements in Vadsø include Ekkerøy, Kiby, Krampenes, Skallelv, Valen, and Vestre Jakobselv.
The municipality is the 83rd largest by area out of the 356 municipalities in Norway. Vadsø is the 170th most populous municipality in Norway with a population of 5,568. The municipality's population density is and its population has decreased by 9.1% over the previous 10-year period.
The village of Vadsø was granted town status in 1833. In 1838, the town of Vadsø and the entire rural district surrounding the Varangerfjorden were established as the new municipality of Vadsø (see formannskapsdistrikt law). The law required that all towns should be separated from their rural districts, but because of a low population and very few voters, this was impossible to carry out for the municipality of Vadsø in 1838. (This was also true in the towns of Hammerfest and Vardø.)
In 1839, the western district (population: 598) was separated to become the new municipality of Nesseby. This left Vadsø with 388 residents. In 1858, Vadsø municipality changed again: Nesseby Municipality (population: 706) was merged back into Vadsø and the district of Vadsø located south of the Varangerfjorden (population: 1,171) was separated to form the new municipality of Sør-Varanger. This change resulted in a population of 2,050 in Vadsø municipality. In 1864, the western district of Nesseby (population: 866) was separated into a separate municipality once again, leaving Vadsø with 1,367 residents.
On 1 January 1894, the rest of the rural district (population: 1,296) surrounding the town of Vadsø was separated to form the new municipality of Nord-Varanger. This left just the town of Vadsø remaining in the municipality of Vadsø which now had 1,114 residents. During the 1960s, there were many municipal mergers across Norway due to the work of the Schei Committee.