The term 'Soil Biology', the study of organism groups living in soil, predates 'Soil Ecology', the study of interactions between soil organisms as mediated by the soil physical environment. Soil Ecology evolved between the late 1950's and the 1970's from research at Oak Ridge National Laboratory, Michigan State University, Colorado State University and the University of Georgia, coincident with the International Biological Program which emphasized understanding processes that define ecosystems. By 1990, many Universities offered courses in soil ecology, emphasizing organism community structure, nutrient cycling, system productivity, physiology and biochemistry of organism groups and their interactions. The chapter is aimed at university-level, and other educated, scientifically-minded readers. The volume should appeal to high school, colleges and universities, in fact, wherever a reference source is needed.