Synopsis Groundwater modeling is an established tool to study the aquifer response for given input-output stresses. In many countries, pollution is an important component of the groundwater problem. Mass transport modeling in recent time helps to understand the migration behavior of pollutant in the saturated and unsaturated region. In recent years, a number of universities and research institutes in India and other developing countries have started to use groundwater flow and mass transport models as groundwater management tools. But there is no book written from any developing country exclusively on modeling which covers the entire gamut of multi-layer simulation, mass transport, fracture flow modeling, measures to contain groundwater pollution, feasibility of artificial recharge to augment groundwater resources and their management through the application of scientific and community participation approach. The aim of the book is to provide more practical ways of modeling the aquifer system by making use of available methods rather than dealing with more mathematical equations and solution techniques for which a number of books and reports are available and referred here. Model calibration process, which is the critical factor of groundwater modeling, has been elaborated alongwith statistical error analysis.