This course book was prepared in support of a training course on fisheries comanagement in Indonesia. It introduces the principles and practice of fisheries co-management with the objective of improving knowledge and skills to successfully develop fisheries co-management institutions. The course book is composed of four main modules which specifically address the fundamentals of fisheries co-management, its theoretical structure and the process of starting, planning and implementing fisheries co-management, all with a focus in Indonesia. From the numerous examples provided in this book, it is obvious that fisheries co-management has the potential to contribute to almost every sphere of fisheries management in Indonesia. It has a potential to incorporate the ecosystem approach and has proved to be effective in promoting conservation activities, including the protection, mitigation and rehabilitation of natural resources. There is a discussion of the criteria which may be used to assess a fisheries co-management regime in their relation to the type of aquatic ecosystem, the exploited species, the existing socio-political and economic system, and the prevailing rules and regulations. Attention is given to how the decision-making process takes place and the roles and responsibilities of the main stakeholders in co-managing fisheries, namely the community users of fisheries resources and the government. The book pays particular attention to the theory and benefits of community organization as a basis for successfully implementing co-management on the ground. The process of organization involves education, empowerment, developing or revitalizing values and ethics systems, developing notions of independence and partnership, developing organizational and leadership skills, and assisting the community to take action. The participatory action research approach methodology applied to fisheries co-management is outlined. Co-management assessment through monitoring and evaluation procedures is described in detail. Finally, the main aspects of how to develop a fisheries management plan are elucidated using examples from rural areas in Indonesia where fisheries co-management has successfully been implemented.