This report presents the results of South Africa's National Biodiversity Assessment (NBA) 2011, which was led by the South African National Biodiversity Institute (SANBI) in partnership with a range of organisations, involving wide participation from stakeholders, scientists and biodiversity management experts throughout the country over a three-year period. The NBA 2011 assesses the state of South Africa's biodiversity, across terrestrial, freshwater, estuarine and marine environments, emphasising spatial (mapped) information for both ecosystems and species. It synthesises key aspects of South Africa's biodiversity science, making it available in a useful form to policymakers, decision-makers and practitioners in a range of sectors. The NBA is central to fulfilling SANBI's mandate in terms of the National Environmental Management: Biodiversity Act (Act 10 of 2004) to monitor and report regularly on the state of biodiversity, and includes two headline indicators that are assessed across all environments: ecosystem threat status and ecosystem protection level. The NBA 2011 also deals with species of special concern and invasive alien species, presents new work on geographic areas that contribute to climate change resilience, and provides a summary of spatial biodiversity priority areas that have been identified through systematic biodiversity plans at national, provincial and local scales. The NBA 2011 will inform the revision and updating of key national biodiversity policies and strategies, including the National Biodiversity Strategy and Action Plan, the National Biodiversity Framework and the National Protected Area Expansion Strategy. In addition, information from the NBA can be used to streamline environmental decision-making, strengthen land-use planning, strengthen strategic planning about optimal development futures for South Africa, and identify priorities for management and restoration of ecosystems with related opportunities for ecosystem-based job creation.