Curitiba is a large size Brazilian city rightly famous for the quality of its transport policy. This policy, apparently straightforward and unexpensive, has been quoted very often as an example for the cities of the developing countries. However, up to now, no other city has been able to fully implement it. The explanation holds on two ingredients that have always been neglected in the numerous reports and articles on the Curitiba model: a specific political and institutional framework on the one hand and an unexpected role for the local planning agency on the other hand. This paper describes the Curitiba model; it also explains the rather specific political and institutional conditions that allowed the effective implementation of this policy in Curitiba (namely the absence of strong economic actors and a remarquable continuous filiation between politicians and bureaucrats throughout the period); it finally insists upon two key functions that any local planning agency should no neglect: monitoring and propaganda.