"Sustainable and efficient use of fisheries resources is closely linked to the legitimacy of fisheries management schemes. Legitimacy depends on the content of the rules and the participation of user-groups in the decision-making process. The paper analyzes the organization of the fisheries management system, in particular the influence of user-participation in decision-making. Theories of common property resources and institutions are adapted to fisheries and a framework for the analysis of co-management institutions is developed. Two Danish case studies of user-participation are examined to analyze how co-management arrangements are functioning and how they impact on efficiency, equity and sustainability of fisheries resources exploitation."