This chapter is an introductory chapter. It broadly outlines this book's central contention—that is, following Alfred Marshall's retirement, the style of economic thought associated with Marshall evolved in an adaptive way through the work of his successor Arthur Cecil Pigou and, notwithstanding the many differences in Marshall's and Pigou's representations of economic theory, Pigou's economics continued to fall within the broad category of a Marshallian "thought style". The general historiographical approach taken is outlined and a brief review of each chapter is provided to orient the reader to the structure of the book.