Rangelands are geographical regions dominated by grass and grass-like species with or without scattered woody plants, occupying between 18-23% of world land area excluding Antarctica. Rangelands are home both to significant concentrations of large mammals and plants with a high value in both leisure and scientific terms and to human populations that have historically been excluded and marginalised, pastoralists and hunter-gatherers. This review looks at the scientific issues in the assessment of rangeland biodiversity and their implications for policy especially in the context of the implementation of the Convention on Biological Diversity.