Book excerpt: First comprehensive survey of how kinship rules were discussed and applied in medieval England. Two separate legal jurisdictions concerned with family relations held sway in England during the high middle ages: canon law and common law. In thirteenth- and fourteenth-century Europe, kinship rules dominated the lives of laymenand laywomen. They determined whom they might marry (decided in the canon law courts) and they determined from whom they might inherit (decided in the common law courts). This book seeks to uncover the association between the two, exploring the ways in which the two legal systems shared ideas about family relationship, where the one jurisdiction - the common law - was concerned about ties of consanguinity and where the other - canon law - was concerned toadd to the kinship mix ties of affinity. It also demonstrates how the theories of kinship were practically applied in the courtrooms of medieval England. SAM WORBY is a civil servant and independent scholar.