The objective of this book is to present the methodology and procedure for constructing complete
conceptual and mathematical models
of two types of problems: (1) groundwater flow, and (2) groundwater contaminant transport, both in the saturated and unsaturated zones. The construction of such models, however, is not the ultimate goal. In fact, these models are used as essential tools for the planning and management for sustainable use of groundwater resources. This use of models is based on our belief that the physical reality can be represented by mathematical models, albeit with acceptable approximations. In this chapter, we examine the concept, process, and limitations of modeling.