This chapter introduces the book’s main themes. It explains why public health policy matters, and why public policy requires ethical and philosophical reflection. It introduces debates around the definition of disease and illness, and debates about the definition of public health. It examines why public health was initially largely excluded from the purview of medical ethics and bioethics in the 1960s and following decades, and some of the drivers behind the rise of ethical reflection on public health since 2000. It also briefly introduces the structure of the rest of the book.