Processing Modflow is one of the most complete three-dimensional groundwater and transport simulation systems in the world. The text and the companion full-version software (PMWIN) offer a totally integrated simulation system. PMWIN comes with a professional graphical user-interface, supported models and programs and several other useful modeling tools. The graphical user-interface allow one to create and simulate models with ease and fun. It can import DXF- and raster graphics and handle models with up to 1000 stress periods, 80 layers and 250,000 cells in each model layer. The model tools include a Presentation Tool, a Result Extractor, a Field Interpolator, a Field Generator, a Water Budget Calculator and a Graphic Viewer. Book targeted at novice and experienced groundwater modelers. The typical user is working as a hydrogeological or environmental consultant, in a water company, in a regulatory agency or a university.