Who is taking important decisions in your projects? Traditionally, all important strategy, structure, and work-design decisions, as well as most of the ongoing decisions about work procedures have been taken by organizational management. Yet, as Tayloristic habits are disappearing, organizations willingly (or unwillingly) change their decision-making approaches to enable more participation and influence from the performers, which gave rise to participation-based parallel organizational structures, such as quality circles, task forces or communities of practice. The latter is the central topic of this talk. A community of practice (CoP) is usually a group of people with similar skills and interests who share knowledge, make joint decisions, solve problems together, and improve a practice. Communities of practice are cultivated for their potential to influence the knowledge culture and bring value for individuals, teams, projects, and organization as the whole. Despite the assumed benefits, implementing successfully functioning CoPs is a challenge, and even more so in large-scale distributed contexts. In this talk, you will learn what helps to run successful communities of practice, based on the findings from studying member engagement in large-scale distributed communities of practice at Spotify and Ericsson.