Models implementation: A state of the art

“Why are so many models designed and so few used” is a question often discussed within the Operational Research (OR) community. The formulation of the question seems simple, but the concepts and theories that must be mobilised to give it an answer are far more sophisticated. Would there be a selection process from “many models designed” to “few models used” and, if so, which particular properties do the “happy few” have? This paper first analyses the various definitions of “models” presented is the OR literature and proposes a synthesis of the functions a model can handle. Then, the concept of “implementation” is defined, and we progressively shift from a traditional “design then implementation” standpoint to a more general theory of a model design/implementation, seen as a cross-construction process between the model and the organisation in which it is implemented. The organisation is, consequently, considered not as a simple context but as an active component in the design of models. This leads to logically propose six models of model implementation: the technocratic model, the political model, the managerial model, the self-learning model, the conquest model and the experimental model.