Soil is a complex body that exists as many types, each with diverse properties that may vary widely across time and space as a function of many factors. This complexity makes the evaluation of soil quality much more challenging than that of water or air quality. Evaluation of soil quality now considers environmental implications as well as economic productivity, seeking to be more holistic in its approach. Thus, soil quality research draws from a wide range of disciplines, blending the approaches of biologists, physicists, chemists, ecologists, economists and agronomists, among others. This book presents a broad perspective of soil quality that includes these various perspectives and gives a strong theoretical basis for the assessment of soil quality. A short glossary provides definitions for terms used throughout the book.