Over many decades, educators have developed countless interventions and theories about how to create lasting change. Implementation research is the study of these efforts with a set of basic questions: What are we doing? Is it working? For whom? Where? When? How? And, Why? In other words, implementation research is an endeavor to understand if and how educational efforts are accomplishing their goals. This chapter describes the landscape of implementation research, tracing it back to its historical roots and connecting it to other fields with the aim of identifying common threads across diverse efforts. The authors survey where the field is today and highlight different perspectives on complex questions that have long troubled researchers. They outline some of the sticky issues ahead and make a case for shared conceptual clarity and clearly communicated and understood language that will help researchers understand how various bodies of implementation research work are related. The authors conclude by describing the opportunity presented to the education research community in this moment: to capitalize on and learn from historical and contemporary work in education and other fields, and to identify connections across theories and approaches and find ways to collectively move forward toward the shared goal of making education better.