This article provides an analysis of the Collaborative Action Research Network's (CARN) origins and development since its foundation in 1976. The author brings the unique perspective of active involvement in CARN almost from its inception, and editorship for many years of its journal "Educational Action Research". 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 author argues that CARN's origins in teachers' action research in classrooms have given it a unique educational base. This has been carried forward to embed learning and educative values in its increasingly broad membership across the professions and within communities since the 1980s. The article explores some of the disruptions and contradictions in CARN over the years; for example, when it changed its name to broaden its membership, and on occasions when its inclusive, voluntarist values have come into conflict with the imperative to remain financially viable. CARN's strength is that it promotes flexibility and tolerance and works to be inclusive of a wide range of methods and approaches that espouse action research principles. CARN is a forum for critical questioning rather than a platform for a critical orthodoxy. It has established a presence and a history, and exists for action researchers to make use of its affordances. The article concludes with an agenda for future development. (Contains 1 figure and 9 notes.)