This book explores pre- and extra-marital relationships among the gentry and nobility in the north of England from 1450 to 1640: the keeping of mistresses, the taking of lovers, the birth of illegitimate children and the fate of those children. As the first comprehensive account of this important aspect of the lives of the elite, it opens up new perspectives on some of the key actors in late-medieval and early modern England. The book draws on a wide range of sources, including court records, wills, property transactions and works of literature. It challenges assumptions about the extent to which sexual activity outside marriage (and consequent bastardy) declined in the period, and hence about the impact of Protestantism, the 'reformation of manners' and other changes to the culture of the elite. In sum, it makes a major contribution to the literature on marriage and sexual relationships, on family and kinship and their impacts on wider social networks, and on gender. The gentleman's mistress is aimed at an academic readership interested in social and political history, including second- and final-year undergraduates. At the same time, its vivid accounts of the personal relationships of the medieval and early modern elite will appeal to a wider popular readership.