The nations of the world have set themselves a target of reducing the rate of biodiversity loss by 2010. Here, we propose a biodiversity intactness index (BII) for assessing progress towards this target that is simple and practical - but sensitive to important factors that influence biodiversity status - and which satisfies the criteria for policy relevance set by the Convention on Biological Diversity. Keywords: Biodiversity, Biodiversity intactness index, Biological diversity, Ecosystems, Taxonomic group.