Modelling is not just about producing results through running a simulation model. It is a social activity, involving many people (other researchers, managers, local people) who are able to contribute to the formulation of a model, but who have no wish to model themselves. Because of Simile's intuitive interface, including familiar, every-day concepts such as stock, flow, influence and object, many people are able to contribute to the model-design process; while the modeller knows that the result of the conceptual-modelling phase can be gradually fleshed out to produce a fully-defined model.