THE APPLICATION OF A DECISION-MAKING MODEL TO HISTORICAL DATA, by W.E. SARIS and I.N. SARIS-GALLHOFER During the preparatory phase which preceded the Cambrai peace agreement concluded in 1529 between Francis I and Charles Quint, the latter corresponded secretly with his aunt, Margaret of Austria regent of the Netherlands, about the nature and importance of what was at stake in the coming negotiations. What claims should be presented to the adversary ? What strategy should they adopt in the negotiations, bearing in mind the chances that their various demands had of being met ? At what point should they make their offers ? At the start or not until the peace conference ? On the basis of information gleaned from this secret correspondence, the object is to discover whether the Emperor and the regent of the Netherlands reached their decisions by means of a rational process. An attempt is made to prove this using a mathematical model. Since the documents revealed that the Emperor and Margaret of Austria were aiming at optimum gains, the model used must be based on the maximisation of utility : the criterion of a rational decision is defined in this model by the choice of the optimum strategy. [Revue française de science politique XXV (3), juin 1975, pp. 473-501.]