During the four decades since the founding of the National Center for Developmental Education (NCDE; originally the Center for Developmental Education), research related to the field has continued to expand and mature. As a research center focused on using research to inform and improve practice, the NCDE's 40th Anniversary timeline presents annotations of ten impactful research studies from each decade from 1976 through 2016. The authors have defined "impactful research" as investigations that provided important information to influence and direct practice in the field. Their definition of developmental education is the integration of courses and services guided by the principles of adult learning and development. This view of the field as the overarching structures, services, and programs to support and teach underrepresented students in postsecondary education--rather than courses to address academic skills gaps only-- guided the selection of research studies represented on the timeline.