This article provides an analysis of the Collaborative Action Research Network's (CARN) origins and development since its foundation in 1976. Cultural-historical activity theory is used as an analytical framework: key concepts are succinctly summarised and then used to identify and explore CARN's agency in developing educational action research. The article focuses on key themes of CARN's activity, such as developing teachers' knowledge as an engine of school reform, establishing an action research literature and supporting the challenging processes of collaboration. The article explores some of the disruptions and contradictions in CARN over the years. The article concludes with an agenda for future development.