Incest was a social problem in the Middle Ages, and also a popular literary theme. This wide-ranging study is the first survey of medieval incest stories in their cultural context. Did they reflect real life situations? How was incest defined in the Middle Ages? How were classical incest stories treated by medieval writers? Why was incest such a popular motif in the legendary lives of popes and saints, and why was it inserted into the stories of great heroes such as Charlemagne and Arthur?