The Economics of Ecosystems and Biodiversity (TEEB) aims to promote a better understanding of the true economic value of ecosystem services and to offer economic tools that take proper account of this value. TEEB is in two phases and this interim report summarizes the results of Phase I. It demonstrates the huge significance of ecosystems and biodiversity and the threats to human welfare if no action is taken to reverse current damage and losses. Phase II will expand on this and show how to use this knowledge to design the right tools and policies.