The simulation of networks and distributed systems is a means to analyze and evaluate protocols in a quick and cost-efficient way and is therefore a valuable tool in the research of networks and distributed systems. While analytical approaches are often challenged by the complexity of scenarios and field tests are challenged by a high hardware configuration effort and resulting costs, simulations allow for the efficient investigation of the parameter space regarding network topologies, communication patterns and dependencies to other protocols. However, simulation results are only of relevance if the modeling and evaluation  has been done accurately. Therefore, the lecture provides the required basics in mathematics and algorithms,  practical experience in the use of simulators and simulation tools as well as an illustration of how simulations can be applied to answer recent research questions,e.g. in the field of vehicular networks or social networks.