ActKM is a Community of Practice for people interested in public sector Knowledge Management. Having begun in 1998, the community now numbers more than 550 members and is nurtured and maintained predominantly, but not exclusively, on-line. Utilising the Cynefin sense-making framework, this chapter analyses the ActKM community and provides a practical account of its history, purpose, guiding principles, goals, characteristics and dynamics. The chapter concludes with a summary of the lessons learnt from the ActKM experience that others might find useful in cultivating a vibrant Community of Practice of this type.