The eight levels of biological classification are domain, kingdom, phylum, class, order, family, genus and species. These levels are an important part of taxonomy, which is the science of identifying species and organizing them according to systems of classification.
Domain and kingdom are the broadest taxonomic classifications available. All animals belong to the kingdom Animalia, but each species has different characteristics. Genus and species are the most narrow classifications available.
Each taxonomic level has unifying features. Organisms in the phylum Chordata, for example, all have a spinal cord. Members of the class Mammalia nurse their young.
Taxonomic classification allows scientists to identify natural patterns and explain how organisms are related to each other.