The First Swedish Crusade is a legendary military expedition presumably in the 1150s that has traditionally been seen as the conquest of Finland by Sweden, with pagan Finns converting to Christianity.

According to the legend, the crusade was conducted by King Eric IX of Sweden.

Bishop Henry of Uppsala accompanied him and remained in Finland later to become a martyr there.

The actuality of the crusade is debated amongst academics.

No archaeological data give any support for it, and no surviving written source describes Finland under Swedish rule before the end of 1240s.

Furthermore, the diocese and bishop of Finland are not listed among their Swedish counterparts before the 1250s.