This chapter introduces the central arguments presented in the book and establishes the scope and context of the study. The discussion includes a detailed overview of the historiography of illegitimacy in Britain, with attention drawn to the ways in which the field has developed over the last four decades, highlighting major methodological developments. The methods and approaches used in the book, which combine quantitative and qualitative methods that reveal both broad patterns and individual experiences, are also introduced. The range of primary sources and the approaches used throughout the book are also discussed, with an emphasis on how they relate to the book’s key research questions throughout. Sources include parish registers, poor law accounts, bastardy bonds, filiation orders, court records, Welsh-language ballads and ecclesiastical licences. This chapter concludes with a brief discussion of the emergence of the concept of illegitimacy as a social problem in the eighteenth century, the legacy of which is still evident in modern critiques of single motherhood.