Documents related to sexual crimes committed by Saracen women, subjects of the Christian kings of the Iberian Peninsula, show to what extent a medieval legal norm could differ from legal practice. These crimes mostly included sexual liaisons with Christian men. Sexual contacts between Christians and non-Christians were prohibited by European Christian law. There was no unified norm in the Aragonese lands in the 14th century; provisions of canon law, and local law were thought to be enough. Islamic law, it its form that was practiced in the Aragonese lands in the 14th century, saw extra-marital sex as a serious offence. According to the norms of Sharia law adultery was punished by stoning, and fornication — by 100 lashes; other punishments included banishment for a year. The ‘Llibre de la Çuna e Xara’, a legal code compiled in a seigneurial domain of the Kingdom of Valencia in the 15th century., demonstrates the preservation of these norms. In practice, however, Muslim women found guilty of having sex with Christian men were not punished in this way, but usually made slaves to the royal treasury. The King and his officials benefited from this practice, which made it possible to exploit human resources and get a ransom payment. Thus, the royal curia paid a good deal of attention to accusations of sexual contacts between Muslim women and Christian men. Cases were taken from the jurisdiction of cadies as serious crimes of mixed type and were send to higher courts: the courts of royal officials, or to the royal curia itself. The author concludes that in the Middle Ages, the dichotomy of norm and practice could result from a situation when central authorities created a new legal practice, which was developed as a custom and had a status of a custom, not a written norm.