The importance of verification, validation and documentation of simulation models is widely recognised, at least in principle. However, in practice, inadequate model management procedures can lead to insufficient information being available to allow a model to be applied with confidence or for it to be re-used without difficulty and much additional effort. The ease with which a model can be understood by someone not involved in its development depends on the transparency of the model development process. This paper reviews ideas associated with transparency and model management. It also includes discussion of some related issues that are believed to be particularly important, such as identifiability and experimental design for model validation. Some recent developments in engineering applications and in physiological and health-care modelling are discussed, along with the responsibilities of the academic community in giving more emphasis to simulation model testing and transparency.