In this chapter, we present some possible applications inwhich numerical modeling can be applied to solve practical problems. However, we need to consider that these examples are simplified, especially regarding geometry and data variability. We often assume homogeneous and isotropic aquifers to show the principal behavior of aquifers caused by stresses such as pumping. In many situations, this leads to solutions that are adequate for preliminary observations. However, we must recognize that there may be more subtle complexities inherent to real world conditions, e.g., in which parameter values are complex functions of space and time. The problems may become ill-posed, so that solutions to these problems are no longer unique. Together with the knowledge of the sensitivity of the modeling result to the different parameters’ values and distributions, in practice, we will obtain a set of possible modeling solutions from which we need to select the one, which best describes the real world problem.