Ecosystem services are the benefits provided by ecosystems that contribute to making human life both possible and worth living. Examples of ecosystem services include products such as food and water, regulation of floods, soil erosion and disease outbreaks, and non-material benefits such as recreational and spiritual benefits in natural areas. The term ‘services’ is usually used to encompass the tangible and intangible benefits that humans obtain from ecosystems, which are sometimes separated into ‘goods’ and ‘services’.

Some ecosystem services involve the direct provision of material and non-material goods to people and depend on the presence of particular species of plants and animals, for example, food, timber, and medicines. Other ecosystem services arise directly or indirectly from the functioning of ecosystem processes. For example, the service of formation of soils and soil fertility that sustains crop and livestock production depends on the ecosystem processes of decomposition and nutrient cycling by soil micro-organisms.

Some scientists have advocated a stricter definition of ecosystem services as only the components of nature that are directly enjoyed, consumed, or used in order to maintain or enhance human well-being. Such an approach can be useful when it comes to ecosystem service accounting and economic valuation. This is because some ecosystem services (e.g. food provision) can be quantified in units that are easily comprehensible by policy makers and the general public. Other services, for example, those that support and regulate the production levels of crops and other harvested goods, are more difficult to quantify. If a definition based on accounting is applied too strictly there is a risk that ecosystem service assessment could be biased toward services that are easily quantifiable, but with inadequate consideration of the most critical ones for human well-being.

Since ecosystem services are defined in terms of their benefits to people it should be recognised that ecosystem services are context dependent, that is, the same feature of an ecosystem can be considered an ecosystem service by one group of people but not valued by another group.