SummaryNatural and artificial systems of classification are defined. One of the most advanced natural systems of classification is the Periodic Classification of the Elements and its development is traced so that it can be used as a framework of reference for other systems of classification, in particular those for plants and soils. It is demonstrated that plant classification is also a mature system, but soil classification is still in an elementary stage of development. The strengths and weaknesses of two recently published systems, the Soils of Europe by Kubiena and the 7th Approximation by the Staff of the U.S. Soil Survey, are discussed.