This chapter will discuss in detail simulation models for emulating and evaluating a system. In this chapter, the author will first introduce simulation techniques used for emulating and evaluating a system in Section 8.1. The selection of appropriate simulation tools along with their advantages and disadvantages will be also discussed. Simulation models of a typical system will be presented in Section 8.2. Detailed steps and phases of a simulation study will be outlined in Section 8.3. Simulation examples will be then provided in Section 8.4 to show the effectiveness of network simulation models.