This Science Plan is mainly concerned with the current extinction crisis on Earth, which, unlike its predecessors, is occurring at an unprecedented rate, is the direct result of human activities and is occurring at all levels at which diversity is measured - from the genetic diversity of many natural and domesticated species to the diversity of ecosystems and landscapes, through the tremendous richness of species. Current human-induced rates of species extinction are estimated to be about 1,000 times greater than past background rates. Biodiversity is the variety of life on Earth. Scientists commonly measure and describe this variety at the level of genes, species and ecosystems, but scientific interest in biodiversity goes far beyond describing and measuring it. The DIVERSITAS programme was founded to address the scientific questions that need to be answered in order to understand how biodiversity supports life on Earth, what the impacts of the present loss of biodiversity are for human and ecosystem survival and how humans can sustainably use and conserve biodiversity.