This analysis of royal marriage cases across seven centuries explains how and how far popes controlled royal entry into and exits from their marriages. In the period between c.860 and 1600, the personal lives of kings became the business of the papacy. d’Avray explores the rationale for papal involvement in royal marriages and uses them to analyse the structure of church-state relations. The marital problems of the Carolingian Lothar II, of English kings – John, Henry III, and Henry VIII – and other monarchs, especially Spanish and French, up to Henri IV of France and La Reine Margot, have their place in this exploration of how canon law came to constrain pragmatic political manoeuvring within a system increasingly rationalised from the mid-thirteenth century on. Using documents presented in the author’s Dissolving Royal Marriages, the argument brings out hidden connections between legal formality, annulments, and dispensations, at the highest social level.