Tornio is a city and municipality located in the Lapland region of Finland. It sits on the border with Sweden, forming a cross-border twin city arrangement with Haparanda on the Swedish side. The municipality covers an area of 1,348.83 square kilometres, including significant water bodies, and serves as a centre of education for Western Lapland with vocational and applied sciences institutions.

The town received its charter from King Gustavus Adolphus on 12 May 1621, officially founding it on the island of Suensaari. At that time, it was the northernmost city in the world and the richest town in Sweden due to its role as the hub of Lapland trade. The border was later drawn through the Torne River in 1808, splitting the region and causing Tornio to become unilingually Finnish after previously having a Swedish-speaking population.

The historic wooden church constructed in 1686 remains a key landmark, having survived the Lapland War due to rapid liberation by Finnish forces. The city centre is situated on the international border, with the modern market square straddling the line between Finland and Sweden. A shared golf course also lies astride the border, highlighting the unique geographical integration of the twin cities.

Tornio attracts visitors through its border trade, tourism based on the proximity to Haparanda, and opportunities to view the northern lights. The area is known for its summer destination appeal, although many services close during winter. The region also offers access to polar day phenomena in June, though it does not experience polar night, providing distinct seasonal experiences for travelers.

The population was 21,018 as of 2023. The economy relies on the Outokumpu stainless steel mill and tourism, with the mill being a major employer in the Nordic countries. Transport includes the Kemi-Tornio Airport and rail connections via Tornio-East station, while Highway 29 serves as the world's northernmost motorway. The climate is subarctic, tempered by sea proximity.