Periodic points for birational mappings of P2

We give a sufficient condition for the existence of periodic points for birational mappings of CP2. Under this assumption, we get a precise estimation of the number of periodic points with a given period. We give an application of this result to the study of the dynamics of these mappings, by computing explicitly the self-intersection of their associated natural invariant current. Our results essentially rely on Bezout's theorem on intersection of hypersurfaces in the complex projective space, and on the precise study of intersection multiplicities.