Protected areas spearhead our response to the rapidly accelerating biodiversity crisis. However, while the number of protected areas has been growing rapidly over the past 20 years, the extent to which the world’s protected areas are effectively conserving species, ecosystems, and ecosystem services is poorly understood. Highlights new techniques for better management and monitoring of protected areas Sets guidelines for the decision making processes involved in setting up and maintaining protected areas Fully international in scope and covering all ecosystems and biomes