The thesis deals with the presence of crusading ideology in medieval Sweden and its political impact. In old Swedish historiography the conquest of Finland was ascribed to three Swedish crusades taking place in 1156, 1249 and 1293 respectively, the subsequent wars with the Russian city-state of Novgorod being seen in extension of this. Lately historians have favoured a more skeptical approach, casting doubt on the significance of crusading ideology in medieval Sweden. The thesis attempts to re-examine the source material and shed some new light on the relative importance of crusading ideology and its political ramifications. The chapters deal chronologically with the alleged first to third crusades, then the crusade of King Magnus Eriksson in 1348, before arriving at some conclusions concerning the central issues, the result being a modification of established views.