Ecosystem services are benefits to humans from the natural environment. These benefits that humans derive from ecosystems are the tangible connection between society and the natural environment. Some of these benefits are timber harvesting, rangeland grazing, municipal water use, carbon sequestration, and pollinators—all discussed in this chapter. The typology developed by the 2005 Millennium Ecosystem Assessment (box 13.1) defines four broad categories of ecosystem services that help to organize our understanding of the relationship between natural resources and human benefits. Although this approach obscures complex relationships between natural and human systems, two important caveats are relevant to discussions of ecosystem services and anticipated climate change effects. First, these categories are not exclusive, and many natural resources fall under multiple categories depending on the context. For example, the consumption of water can be considered a provisioning service, the process of purifying water a regulating service, the use of water for recreation a cultural service, and the role of water in the life cycle of organisms a supporting service. Second, these categories are interdependent, such that individual services would not exist without the functioning of a broad set of ecosystem services.