Tiomila or 10-mila is an orienteering race held annually in Sweden since 1945, usually in late April or early May. It is a 10-man relay which includes both night and daytime legs. The women's race consists of five daylight legs. Tiomila attracts club teams from all the major orienteering nations. In 2008, both the men's and the women's race consisted of about 350 teams. In 2019, there were 336 women's teams, and 310 men's teams.

Orienteering is a group of sports that involve using a map and compass to navigate from point to point in diverse and usually unfamiliar terrain whilst moving at speed. Participants are given a topographical map, usually a specially prepared orienteering map, which they use to find control points. Originally a training exercise in land navigation for military officers, orienteering has developed many variations. Among these, the oldest and the most popular is foot orienteering. For the purposes of this article, foot orienteering serves as a point of departure for discussion of all other variations, but almost any sport that involves racing against a clock and requires navigation with a map is a type of orienteering.