In the mid-ninth century, Francia was rocked by the first royal divorce scandal of the Middle Ages: the attempt by King Lothar II of Lotharingia to rid himself of his queen, Theutberga, and replace her with Waldrada, the mother of his children. Lothar, however, faced opposition to his actions; kings and bishops from neighbouring kingdoms, and eventually the pope himself, were gradually drawn into a crisis affecting the fate of an entire kingdom and which helped durably shape European politics and culture. This is the first professionally published translation of a key source for this extraordinary episode: Archbishop Hincmar of Rheims's De divortio Lotharii regis et Theutbergae reginae. Surviving in a single manuscript produced under Hincmar's own guidance, On the divorce of King Lothar and Queen Theutberga offers eye-opening insight not only on the political wrangling of the time (in which Hincmar was a major participant), but also on early medieval attitudes towards a host of issues including magic, penance, gender, the ordeal, marriage, sodomy, the role of bishops, and kingship. The translation is cross-referenced to Letha Böhringer's MGH edition and includes a substantial introduction and annotations which put the case into its early medieval context and explain Hincmar's sometimes-dubious methods of argument. The text provides fascinating insights into Carolingian society and will make an ideal source text for many undergraduate courses on medieval gender and sexuality, magic or kingship. It will also appeal to all academics and non-specialists interested in this most lurid of cases.