This chapter examines how member participation and governance shape the performance and sustainability of cooperatives. It identifies four key dimensions of member participation: (1) use of cooperative services or labor contribution, (2) cooperation and solidarity among members, (3) participation in decision-making, and (4) capital participation. Active engagement across these dimensions strengthens both the economic and social functions of cooperatives, while weak participation leads to free-riding, loss of identity, and declining performance. Drawing on social psychology and game theory, the chapter explains why cooperation is fragile in competitive environments and how institutional design—such as transparent rules, sanctions against free-riding, and trust-building mechanisms—can sustain collective action. Case studies, including French retail cooperatives and Korea’s Anseong Medical Welfare Social Cooperative, show how structured committees, mentorship systems, and member–staff collaboration enhance participation and accountability. The chapter contrasts cooperative governance with investor-owned firms. Because cooperatives lack capital-market discipline and concentrate authority through “one member, one vote,” weak member engagement can allow managerial opportunism or internal power imbalances to emerge. Successful governance therefore requires balancing board control and managerial support, combining member representation with professional expertise. Examples of both success (e.g., Mondragon’s network governance) and failure (e.g., the UK Co-operative Group and Saskatchewan Wheat Pool) illustrate how governance design critically affects cooperative resilience, autonomy, and long-term viability.