Two popular simulation techniques are system dynamics and discrete-event simulation. However although widely used there is little guidance in the literature on which technique is appropriate to address a particular problem. This paper contains a review of the characteristics of these two techniques in order to provide guidance on their use. In many circumstances it may be that either technique is appropriate and the decision on which technique to use will be determined by the experience and preferences of the modeller for one or other approach. However there is a particular istinction in the techniques in terms of their approach to modelling. The system dynamics method maps a problem onto a generic structure that can help understanding of the underlying causes behind the behaviour of the system. The discrete-event simulation technique attempts to replicate the structure of the system and then allows performance to be measured under a number of scenarios. These approaches have thus different outcomes in that system dynamics can be used to learn the causes of problems and not just treat the symptoms. On the other hand discrete-event simulation is able to track individual resources through the system, show queuing behaviour and generate metrics of process performance.