Taxonomy is the science of grouping organisms according to their presumed natural relationships. Common names, such as robin and fir tree, are the everyday name given to organisms. Linnaeus (1707 - 1778) developed a system of grouping organism into hierarchical categories.

Linnaeus placed structurally similar organisms into a group he called a species, similar species into a larger group called a genus, and similar genera into a family. Similar families were placed in an order; similar orders, in a class; and similar classes, in a phylum. Finally, Linnaeus placed phyla into either the plant or animal kingdom. Rather than list all several categories in naming an organism, Linnaeus chose to use only the species name - that is, the genus name and the epithet denoting the species. For example, Linnaeus denotes the human species as sapiens. Therefore humans belong to the species Homo sapiens. Linnaeus's system is called binomial nomenclature.

Binomial means "two names." The binomial name of a species is called its scientific name. Botanists use the term division in place of phylum when classifying plants. Scientists are also interested in inferring the phylogeny, or the evolutionary history, of a species. Most taxonomists base their classifications primarily on comparative morphology. Taxonomists usually rely on special books or manuals to aide them. Identification often involves the use of a dichotomous key - a written set of choices that leads to the name of the organism. A phylogenetic tree is a visual model of the inferred evolutionary relationships among organisms. Biosystematics is a form of taxonomy that examines reproductive compatibility and gene flow.

The Kingdom Monera is made up of prokarotic organisms, which lack nuclei and other membrance-bound organelles. The Kingdom Protistsa is made up of eukarotic organisms that lack specialized tissue systems. The Kingdom Fungi is made up of heterotropic unicellular and multicellual eukarotic organisms. The Kingdom Plantae consists of plants, all of which are multicellular and autotrophic. The Kingdom Animialia is made up of eukaryotic, unicellular, heterotropic organisms that obtain nutrients by ingesting food.