To effectively conserve biodiversity, we need to be able to define what we want to conserve, determine where it currently occurs, identify strategies to help conserve it, and track over time whether or not these strategies are working. The first of these items, defining what we want to conserve, is complicated by the remarkable diversity of the organisms themselves. This is a product of the genetic diversity of the organisms, that is, variation in the DNA (deoxyribonucleic acid) that makes up the genes of the organisms.

It can be difficult, in some cases, to establish the boundaries between these levels of diversity. For example, it may be difficult to interpret whether variation between groups of individuals represents diversity between different species, or represents diversity only between different populations of the same species. Nevertheless, in general terms, these levels of genetic diversity form a convenient hierarchy for describing the overall diversity of organisms on Earth.

Similarly, the functional and spatial aspects of biodiversity can also be discussed at a number of different levels; for example, diversity within or between communities, ecosystems, landscapes, biogeographical regions, and ecoregions.