The polyphonic sources of medieval Sweden are very few, although well-documented in musicological research. However, while most of the earlier research has tended to focus on interpreting the sources themselves rather than to examine the cultural and historical context in which they were written, the present dissertation aims at providing a broader narrative of the transmission and practice of polyphony. By examining the cultural context of the sources and putting them in relation to each other, a bigger picture is painted, where also Danish and Norwegian sources are included. Based on the discussion and analyses of the sources, a general historical outline is suggested. The practice of organum in the late 13th century in Uppsala was probably a result from Swedes studying in Paris and via oral transmission brought the practice back home. This 'Parisian path' was accompanied by an 'English-Scandinavian' path, where mostly Denmark and Norway either influenced or were influenced by English polyphonic practice. During the 14th century, polyphony seems to have been rather established in Sweden, although prohibitions against it were made by the Order of the Bridgettines. These prohibitions were probably linked to a general antipolyphonic attitude in Europe, beginning with the papal bull of John XII in 1324. The sources of the 15th and 16th centuries are very different from each other, and perhaps suggest that polyphony of older styles were sung in monasteries and certain churches while more modern discant were sung at the royal courts and at larger religious feasts such as the translation of Catherine of Vadstena.