Ecosystems function like other capital assets – they generate a flow of services through time, and the capital can be held intact if the services are consumed in a sustainable fashion. Moreover, any ecosystem tends to generate many such services. This chapter analyses ecosystems from this multi-functional perspective, making a clear distinction between the total value of the ecosystem as an asset and the value of small or discrete changes in its service flow. The valuation issues are illustrated with reference to the debated benefits of ecosystems as providers of genetic value for pharmaceutical research.