Institutions are considered as ‘rules of the game’ in this chapter, which is informed by two approaches taken to the analysis of institutions in natural resource governance. The first approach centres on viewing co-management itself as an institution. This section draws on common property theory and Ostrom’s design principles for sustainable common property regimes. The section also considers insights from literature on ‘institutional fit’ as a response to scale mismatch to identify lessons for co-management. The second approach is concerned with investigating which institutions shape co-management and how, from formal, bureaucratic institutions of policy and legislation to informal, socially embedded institutions, such as customary systems, kinship ties and gender norms. Critical institutionalism suggests that bureaucratic and socially-embedded institutions may interact through processes referred to ‘institutional bricolage’, with implications for how co-management evolves and performs.