This chapter outlines the theoretical rationale behind the book’s argument that the Pilgrims Society’s activities during the first half of the twentieth century were a nascent form of public diplomacy and that they contributed to the development of later, more official, public diplomacy organisations like the British Council, the Division of Cultural Relations, and the United States Information Agency. In so doing, this chapter analyses the historical orthodoxies surrounding public diplomacy and offers a definition of the concept that will applied across the rest of the book. The chapter also establishes how concepts of public diplomacy, cultural diplomacy, associational culture, and elite networking intersect and why this intersection is important to the Pilgrims Society.