The first quarter of the twenty-first century has witnessed a burgeoning of research, policy, and practice focused on transitions to school. Much of this has been spurred by international attention and national commitments to educational provision, equity, and educational outcomes. The chapters in this book explore the background, contexts, and implications of transitions research, policy, and practice across multiple countries. This chapter introduces the book, outlining its purpose, nature, and scope. It provides an overview of what readers might expect from the book and how they might engage with it. To help set the scene, definitions for what is meant by ‘transitions’ are drawn from various theoretical paradigms and applied to ‘transitions to school’. A brief overview of the state of transitions to school research and policy at the end of the twentieth century from the authors’ own contextual standpoints is provided to set a baseline for the national chapters.