The Collaborative for Academic, Social, and Emotional Learning (CASEL) has produced a five-brief series documenting insights from their efforts to understand how educators and researchers can build relationships that support a shared action research agenda around social and emotional learning (SEL). It shares the perspectives of researchers and practitioners on developing and sustaining collaborative inquiry in classrooms, schools, districts, and states. The goal of the series is two-fold: (1) to articulate an overview of CASEL's research-practice agenda and, (2) to explore our learnings at the school, district, and state level about developing research-practice partnerships (RPPs), action research, continuous improvement, and adult SEL capacity. This first brief in the series summarizes CASEL's history of research, describes an evolution of their research approach, and articulates the plan for their Research-Practice Partnerships (RPPs) across school, district, and state levels of the education system.