Also appears in collection : Exposés de recherche

We will describe a new approach to the study of discrete dynamical systems on the real line, which consists in considering their orbits as "fractal objetcs". In particular, the formal classification of analytic systems can be reproven with this method. We will also explain the main lines of a program devoted to the study of some non analytic systems. These are generated by maps which admit a specific type of transseries (Dulac’s transseries) as asymptotic expansions.