Broodfonds (literally: “bread fund”) is a mutual insurance association in which self-employed jointly make insurance arrangements to cover risks of sickness or disability. What motivates members to join these groups? How important are social aspects like the group composition, cohesion, and trust for the initiative’s success? How should they organize to be sustainable towards the future? These questions are answered by combining abstract experiments and data collected among broodfonds members. The results are used to improve the organization of broodfonds (and other type of commons).