Book excerpt: Soils are receptacles for a wide range of hazardous chemicals generated by human activities. Whether or not this contamination is deliberate, accurate toxicity assessments are important for health and economic reasons. Soil Ecotoxicology discusses the sources, fate, and transport of hazardous chemicals in soils. The fate (biodegradation and modeling) and the potential impacts of pesticides on soil ecosystems are emphasized, and methodologies for performing toxicity assessments are provided.