Taxonomy is the science of classifying organisms.
The purpose of a classification is to provide a natural framework for the organization of the diversity of life. Classification is used in many walks of life, not just biology. For instance libraries classify books in order to allow the patrons to locate the desired book. Based on this last goal, it is a basic principle of taxonomy that the groups established for organisms should be natural, that is they should be consistent with, or based upon, phylogenetic relationships. The following are the main philosophical approaches to taxonomy, or schools of taxonomy as they are usually called.