The development of computer simulation methods has proceeded in parallel with those in other areas of computing. Thus, interest in component-based approaches is evident both in general software engineering and in computer simulation, with advocates arguing that component-based approaches are far superior to more conventional ways of developing software and applications. Potential benefits are reduced cost and development time arising from reuse of components, as well as easier model adaptation due to the features of extensibility and evolvability. If these are to be realised, then organisations must develop ways to ensure that costs and benefits are shared and should ensure that suitable libraries and component distribution frameworks are available. In a simulation context it is also crucial to ensure that the issue of model credibility and validity is addressed even if the components are thought valid.