Background: The social processes that operate in community groups need to be better understood if people with intellectual disability are to be included in such groups. This study aimed to identify the nature and impact of the group processes on the active participation of people with intellectual disability. Method: Extensive field notes were taken during 2 years of participant observation whereby 5 people with a moderate level of impairment were supported to participate as individuals in community groups for periods of 5 to 10 months. Analysis used a critical realist approach. Results: Active participation was influenced by the interaction of 5 key social processes: leadership response, characteristics of the participants with intellectual disability, access to expertise, the presence of an integrating activity, and dealing with the difference dilemma. Conclusions: By revealing these processes, the study identified a number of interventions and ways of approaching community groups that have the potential to increase the extent to which people with moderate levels of impairment become active participants.