This APN project set out to test the ideas that communities can provide accurate forest measurements to estimate and monitor forest C stocks, and that action research is an appropriate approach to develop community-based forest monitoring systems. Research collaborators in Indonesia, Cambodia, Lao PDR, Viet Nam and Papua New Guinea trained local facilitators on forest monitoring and community engagement concepts and techniques. The facilitators in turn provided training and ongoing support on biomass assessment to participating communities. The monitoring systems were elaborated to reflect locational, cultural, institutional and other context-specific factors. Action research was found to be a suitable approach for developing the community-based forest monitoring systems. Community understanding of carbon and of biomass assessment protocols and techniques was built gradually over several years of their engagement in measuring their forests, recording the data and discussing the results with the facilitators. This resulted in some communities taking initiative to promote their forest monitoring within and outside their villages. The action research also provided strong evidence that with appropriate training and ongoing support, communities can provide accurate forest measurements for reliable C stock estimates.