Community-based management of natural resource (CBNRM) projects have commonly failed to deliver conservation and development benefits. This thesis examined how the theoretical assumptions of common pool resource (CPR) theory have contributed to the indifferent performance of CBNRM projects. Evidence was gathered from two CBNRM case studies in Zanzibar to show that CPR institutional design does not sufficiently acknowledge the politics or social relations of project sites. Moreover, these limitations reduce CPR theory's explanatory power and the functionality of CBNRM projects. This is because CPR theory's influence on CBNRM projects is to frame people with fixed identities and related interests as 'rational resource users', rather than people enrolled in multiple network relations with differentiated means of influence, interests and responsibilities. Actor-oriented theory is used to show that CBNRM would benefit from a shift in the correlation with institutional design factors to understanding the operation of power and conflict at project sites. These findings suggest that currently CBNRM projects are too mired in concern about regulating the 'direct' relationship between resource users and conservation objectives, with problematic implications. It is shown that actor-oriented theory is more sensitive to the different capacities, interests and strategies of actors in CBNRM institutional transformation processes. While actor-oriented theory does not offer a parsimonious or predictive theory to reform CPR theory or CBNRM policy, it can provide insights into pre-project conditions and emergent practice useful for explaining project interventions.