With over 90% of mushroom producers having opted to participate in the industry through informal farmer groups, this paper sought to identify the key factors that unify members of informal collective initiatives. In contrast to formal organisations, which are regulated by law, informal groups are fully autonomous and not regulated by any legal instrument in Swaziland. Based on a conceptual framework that uses social capital dimensions to study collective action, trust, cooperation and communication were identified as the key elements responsible for ensuring cohesion in informal groups engaged in mushroom production. Further analysis indicated that trust is positively influenced by gender, age and religion, while cooperation was found to be influenced by members’ dependence on mushrooms for food. Communication, on the other hand, was found to be positively influenced by the level of trust and member cooperation. The empirical evidence indicates that members from communities characterized by positive cognitive social capital are most likely to engage in voluntary collective action in an attempt to improve their livelihoods. The study, therefore, recommends that informal groups developed voluntarily by community members should be encouraged and embraced as an important element of Swaziland’s development agenda.