Soil organic matter (SOM) is a key constituent of soil as it is a "revolving nutrient find" and improves soil structure, maintains crop production and minimizes erosion. In semiarid environments, the major problem for sustainable farming systems is the continuous decline of SOM towards levels too low for agricultural purposes. In this book, the authors present topical research in the study of the ecology, environmental impact and management of soil organic matter. Topics include soil organic carbon stocks and changes due to modifications on land use and management practices in Brazil; the preservation of SOM in semiarid Mediterranean environments; effects of SOM on the transport of non-aqueous phase liquid in soils and soil organic carbon stocks in relation to different land-use types in a mountainous watershed.