In the last few years, the evaluation of large scale applications across mobile wireless networks has raised a crucial challenge to the research community. Simulation modeling methods can be quite powerful in gaining insight into the behavior of complex systems. The main advantages of simulation modeling include the ability to evaluate scenarios not easily achievable through empirical methods (i.e. scalability testing of networks) and the ability to modify models to test system sensitivity and tune performance. Another important application of simulation modeling techniques is to perform meaningful comparative studies of different technologies, protocols, or new implementations to determine which communication technology performs better from the QoS point of view in a specific scenario. Simulation modeling is a crucial step in the design, development, test and evaluation of any network implementation or strategy, providing the necessary support to the usual demand for “what if” analysis and studies in the network environment. This chapter describes a taxonomy of the different simulation techniques available in the market, introduces statistical concepts for validating the results of a simulation study and describes case studies illustrating the role of simulation in wireless network design.