Ecosystems provide important commodities and environmental benefits to society. As such, the management of ecosystems is an economic, social, and political issue encompassing all sectors of an economy. It involves trade-offs between competing uses and users, as well as between additional economic growth, ecosystem protection, and further natural resource depletion and degradation. Any particular use of ecosystems has its opportunity costs, consisting of the foregone benefits from possible alternative uses of the resource, including non-use. Decision-makers are faced with balancing these varied resource uses, for example, between freshwater demands from agricultural irrigation on the one hand, and the desire to protect rivers for fish and wildlife habitat on the other hand. Striking a balance between the trade-offs of economic growth and ecosystem resource use, possibly leading to their degradation and depletion, is crucial for the sustainable management of our natural resources. Economic valuation contributes to an improved natural resource allocation by informing decision-makers on the full social costs of ecosystem exploitation and the full social benefits of the goods and services that healthy ecosystems provide. This chapter addresses the various dimensions of economic and social value, before explaining the different valuation and evaluation techniques in Chapters 6 and 7, respectively.