IUCN, WWF and the US National Oceanic and Atmospheric Administration (NOAA) have developed this guidebook to assist marine protected area (MPA) managers in assessing the performance of their MPA. Based on this assessment, it shows how necessary changes can be made to improve management measures. It presents a flexible approach that can be used in many types of MPA and offers a variety of specific biological, socio-economic and governance indicators to measure the effectiveness of management actions in achieving MPA goals and objectives.