The history of the medieval child murder libel is the history of an idea. At its most basic, that idea is that Jews secretly kidnap Christian children in order to torture and murder them for religious reasons. Ideas, however, are not static. Different local cultural norms and religious contexts influenced and moulded the idea as it spread to new geographical areas. The result is that the idea evolved different versions over time: at first Jews were accused of abusing and crucifying children in a parody of the Passion of Christ, then this accusation was joined by the claim that Jews drained the blood of Christian children to use it for either medicinal or magical reasons. The idea that Jews consumed the blood of Christian children as part of their Passover celebrations also emerged. In Spain, one famous case saw Jews accused of killing a child not to eat its blood but to collect its heart in a demonic scheme to concoct a potion that would kill all the Christians of the Iberian Peninsula.

Tracing the history of this idea and its evolution is a challenging task for a historian. We can confidently point to its origin in twelfth-century England and follow its development but the nature of its transmission across Europe is far less straightforward. Historians have access to chronicles and hagiographies but there is little doubt that the transmission of tales of child murder by Jews often occurred via casual conversations or as stories told and retold in inns, households, churches, and monasteries across many parts of Europe. Most of the written accounts explicitly refer to the oral transmission of the child murder libel. In the twelfth century, Thomas of Monmouth claims to have heard of the conspiracy to murder Christian children from a converted Jew and, in the thirteenth century, the Dominican Thomas of Cantimpré did not hide the fact that his account of the accusation of Pforzheim was based on his conversation with two fellow Dominicans.