The Jómsvikinga saga (JS) is one of the most challenging Old Norse sagas when it comes to the definition of its genre. In this article it is argued that in spite of the entertaining and Active elements that the saga contains, it can be used as a historical source. The saga should be understood as part of contemporary (i.e. sagas and historiographical works written down ca 1200) literary tradition. As previous research has already shown, the JS, together with the Orkneyinga saga and the Fsereyinga saga, belongs to the same "seminal" school of narrative technique, which could explain why these sagas are difficult to categorize. Interestingly, all these three sagas deal with the relationship of the upper class and the king in one way or another, although their setting is different. One reason for this could be that at the end of the 12th century and the beginning of the 13th century we can discern that the power balance was changing between the upper class and the king in Denmark and Norway: the kings were relying now on the rex iustus-ideology, which meant that they based their power on the idea of being the substitute of God on earth. Thus, the kings elevated themselves from the upper class, whereas before they had been just primus inter pares. The historiographical side of the JS can be examined also by looking at some details in the content of the saga. In this article two details are taken as an example. The first one is the beginning of the saga, which concentrates on the history of the Danish Kings. The plot of this part of the saga seems disjointed and it has even been left out by one of the manuscripts (AM 510). However, its presence seems to be an attempt to give a historical framework for the whole saga, which would support the hypothesis that the saga is intended to be understood as history. The other detail that should be studied further is the law of the Jómsvikings which crystallizes the whole heroic ethos of this warrior band. The law should be compared with contemporary bird-laws and law codes for (religious) orders in order to find out whether it is corrupted by these or whether it represents some genuine oral tradition. This kind of study would help to discern possible later additions to the saga. All in all, there seems to be strong support that the JS should be included in the contemporary Old Norse historiographical works, and that the genre-division of the sagas should not be considered as definite and exclusionary when it comes to the study of history. [ABSTRACT FROM AUTHOR]