Simulation has its strengths and its weaknesses as a methodology: there are certain types of problems for which the use of simulation is highly appropriate, likely to produce useful results, and cost-effective; for other types of problems, this is not true. There is nothing unusual about this: no single analytical methodology can deal with all quantitative problems that one may encounter. Nonetheless, simulation has been the subject of an unusual amount of controversy over the last decade or so (when it truly came into its own as a widely used approach). This phenomenon can be attributed to the fact that inherent in the concept and the mechanics of a simulation model or experiment, there is the potential, to an exceptional degree, for misuse of the technique. In this section we discuss briefly some of these issues. Chapter 8 presents a more detailed discussion of the implementation and proper use of models, in general, in urban operations research.