This chapter defines the term “political secularism,” arguing that it is defined in many different and confusing ways. One set of definitions focuses on the relation between religion and government. The other set of definitions lingers on atheism and dislike of religion. The chapter tries to identify “what we talk about when we talk about secularism.” Some of those conversational topics include disputes about (1) state institutions, (2) gender and sexual minorities, (3) religious minorities, and (4) art and expressive liberties. The chapter ends by outlining the goals of the book.