This is the most comprehensive book on mathematical modeling of groundwater flow and contaminant transport. It is written by one of the most highly cited authors of groundwater books (Dynamics of Fluids in Porous Media, and Hydraulics of Groundwater). Its purpose is to construct conceptual and mathematical models that can provide the information required for making decisions associated with the management of groundwater resources, and the remediation of contaminated aquifers. The basic approach of the book is to accurately describe the underlying physics of groundwater flow and solute transport in heterogeneous porous media, starting at the microscopic level, and to rigorously derive their mathematical representations at the macroscopic level. However, the amount of mathematical knowledge required is kept minimal. Occasionally, mathematical help is provided.