Post-harvest fish losses are a major concern and occur in most fishing distribution chains throughout the world. This manual is the result of field testing and validation activities by FAO of three key post-harvest fish loss assessment methodologies developed over the past two decades. Meant as working tool for extension officers, it describes these methods and provides guidance on when and how they can be used in the process of planning an intervention to reduce post-harvest losses or monitoring and the effectiveness of a loss reduction intervention. It also provides the information on data communication and the design of loss reduction intervention to give policy-planners and decision-makers a better understanding of issues facing fishing communities