The editors of What Is Religion? Debating the Academic Study of Religion asked seventeen leading scholars of religion to finish the statement “Religion is . . .” in a sentence or two, at most a paragraph. Their answer then went to another contributor to write an essay based on it (whether as a reply, a critique, or an application), to which the original author of the paragraph then responded in a brief essay. The result is a collection of scholarly conversations among a wide range of scholars selected to represent the breadth of the current field. To this collection the editors have attached a long appendix, modeled on James Leuba’s 1912 appendix to his Psychological Study of Religion: Its Origin, Function, and Future, that includes over thirty classic or contemporary definitions with their own commentary on them.