The prerequisite modelling fundamentals are presented in the first chapter in a manner comprehensible to students as well as to practicing scientists and engineers. The second chapter describes the many environmental processes that lend themselves to modelling, for example pollution and wastewater treatment. The third part of the book provides 65 simulation examples both on the page and on an accompanying diskette in the simulation language ISM - the first time that this has been done with a teaching book in this field - ready-to-run on any DOS personal computer. Crucially, the simulation runs can be interrupted to allow rapid interactive parameter changes and easy plotting of results; this enables the reader to get a feel for the model and system behavior.