The book presents Lesson Play, a novel construct in mathematics education to be used by researchers and teacher educators. Inspired in part by the style of Lakatos’s evocative Proofs and Refutations, Lesson Play features imagined interactions between a teacher and her/his students, presented in the form of a script for dialogue in the classroom. This book offers the first comprehensive survey of the affordances of the Lesson Play tool, particularly in the areas of pre-service teacher education and teacher professional development. It exemplifies an approach to teacher education that seeks to coordinate mathematical and pedagogical dimensions of teaching as they emerge in real classroom settings by focusing on aspects of practice such as teaching moves and classroom discourse.