This book is concerned with modelling the fate of organic substances in the soil. Once a chemical enters the soil it is subject to various transformation processes. It partitions between the liquid, solid and gaseous phase, it is sorbed to different binding sites with a different strength of bonding, it may decay by a simple chemical process or it may be transformed by microorganisms. Solute transport through soil and subsurface is mediated by water flow and is strongly influenced by solute sorption. To complicate matters, soil structures are heterogeneous. All these processes are embedded in a spatio-temporal hierarchy. The book brings together many different aspects of environmental fate modelling of pesticides comprising such diverse subjects as, e.g., compartment theory, nonlinear biological degradation models, modelling toxicity, parameter identification, coupling of physical and biological processes, pedotransfer functions, translation of models across scales, coupling geographical information systems with models, and FUZZY-approaches.