Human population growth, unsustainable development, and their consequences have taken and will continue to take their toll on the world’s biodiversity and natural resources. Establishing and effectively managing protected areas is a cornerstone of in-situ conservation of biodiversity and natural resources. To date, more than 13% of the world’s forest area has been designated primarily for biodiversity conservation, and these forest protected areas are part of a global network of more than 120,000 protected areas established for conservation purposes. Managing protected areas effectively despite development and other pressures has always been a challenge. Here we argue, however, that effective protected area management has become a task of growing complexity because of the following obstacles that have emerged in the recent past: Changing conservation paradigms that expect protected areas to reconcile biodiversity conservation and sustainable developmentChallenging conservation targets that increasingly require protected area managers to measure, monitor, and report on the performance of protected areasGlobal change and climate change, which have begun to exacerbate the impact on protected areas of conventional pressures, and therefore start to challenge the whole concept of in-situ conservation Here we discuss these challenges with the emphasis on forest protected areas and consider the widening gap between what is expected from protected areas and what they can achieve given the resources and support provided. We argue that without the following steps, a great deal of the biodiversity that still exists in protected areas, especially in the tropics, will be lost within a few decades: Re-positioning of biodiversity conservation at the top of political and public agendasSignificant investments in the effective management of protected areasSimilar investments in the establishment of biodiversity-friendly landscapes around protected areas