The Guidebook for evaluating fisheries co-management effectiveness offers a process and method to evaluate the performance of a fisheries co-management system and its plan in order to enhance its effectiveness in delivering benefits and in contributing to environmental, social and economic sustainability and good governance. It is to be used to evaluate the effectiveness of an existing fisheries co-management system operating at a fishery, community or sector level, or in a spatially defined area. It presents a flexible approach that can be used in many types of fisheries management systems with different contexts and characteristics.