Determining the value or worth of biodiversity is complex. Economists typically subdivide utilitarian or use values of biodiversity into direct use value for those goods that are consumed directly, such as food or timber, and indirect use value for those services that support the items that are consumed, including ecosystem functions like nutrient cycling.

There are several less tangible values that are sometimes called non-use or passive values, for things that we don't use but would consider as a loss if they were to disappear; these include existence value, the value of knowing something exists even if you will never use it or see it, and bequest value, the value of knowing something will be there for future generations (Moran and Pearce 1994 [link]). Potential or Option value refers to the use that something may have in the future; sometimes this is included as a use value, we have chosen to include it within the passive values here based on its abstract nature. The components included within the category of "utilitarian" values vary somewhat in the literature. For example, some authors classify spiritual, cultural, and aesthetic values as indirect use values, whiles others consider them to be non-use values, differentiated from indirect use values -- such as nutrient cycling -- because spiritual, cultural, and aesthetic values for biodiversity are not essential to human survival. Still others consider these values as separate categories entirely. (See also, Callicott 1997 [link], Hunter 2002 [link], Moran and Pearce 1994 [link], Perlman and Adelson 1997 [link], Primack 2002 [link], Van Dyke 2003 [link]). In this module, we include spiritual, cultural and aesthetic values as a subset of indirect values or services, as they provide a service by enriching our lives (Table 8.1).