This chapter introduces simulation modelling as an important method for analysing organisational systems. Simulation modelling is explained in terms of its use of a combination of explanatory and descriptive modelling approaches and its characteristic as a dynamic mathematical model which allows changes in system attributes to be derived as a function of time. The simulation modelling approaches of discrete-event simulation (DES), agent-based simulation (ABS) and system dynamics (SD) are then covered with a particular emphasis on the key features of DES. The relevance of DES to analysing organisational systems is established, and example application areas of the method are outlined. This chapter introduces simulation modelling in the context of a systems view of the organisation. The three approaches of SD, DES and ABS are described. The main features of DES are explanatory modelling of the process structure, descriptive modelling of the process elements and the ability to move the model over time. We also cover the use of DES to model the variability and interdependence inherent in organisational systems and present some benefits and limitations of the use of DES.