1911 Encyclopædia Britannica/Jus Primae Noctis

JUS PRIMAE NOCTIS, or Droit du Seigneur, a custom alleged to have existed in medieval Europe, giving the overlord a right to the virginity of his vassals’ daughters on their wedding-night. For the existence of the custom in a legalized form there is no trustworthy evidence. That some such abuse of power may have been occasionally exercised by brutal nobles in the lawless days of the early middle ages is only too likely, but the jus, it seems, is a myth, invented no earlier than the 16th or 17th century. There appears to have been an entirely religious custom established by the council of Carthage in 398, whereby the Church required from the faithful continence on the wedding-night, and this may have been, and there is evidence that it was, known as Droit du Seigneur, or “God’s right.” Later the clerical admonition was extended to the first three days of marriage. This religious abstention, added to the undoubted fact that the feudal lord extorted fines on the marriages of his vassals and their children, doubtless gave rise to the belief that the jus was once an established custom.

The whole subject has been exhaustively treated by Louis Veuillot in Le Droit du seigneur au moyen âge (1854).