This resource provides mathematics educators with tools for conducting Collaborative Lesson Research (CLR), a form of Lesson Study developed out of the original Japanese Lesson Study and intended to improve student and teacher learning. Renowned mathematics education researchers Akihiko Takahashi and Geoffrey Wake bring together educators across the US and UK with first-hand experience using CLR in their schools. Readers will learn the essentials for an impactful Lesson Study directly from the scholars who coined the term, and benefit from the dual perspectives of math education researchers and teachers who have used CLR when reflecting on their own classroom pedagogy. These contributors define CLR and provide examples of successful CLR using real-life case studies, as well as introducing pathways for getting started and practical suggestions for implementation into different school environments. Across these examples, readers will: understand the essence of Lesson Study, considered as CLR, and its important features be advised what participants in CLR should expect to do (observing research lessons, designing lessons, teaching research lessons, facilitating post-lesson discussion, etc.) and provide guidance and support with this enactment be advised on how to develop, embed, and sustain CLR communities preview potential outcomes over time from undertaking CLR Research lesson proposals and plans to support readers in understanding CLR are also included. Ideal for practicing teachers, teacher leaders, teacher educators, and professional developers involved in mathematics teaching, this book offers first-of-its-kind entry points for CLR. Its combination of theory and practice will empower educators to implement this increasingly popular vehicle for understanding students’ learning of mathematics.