Periodic points for birational mappings of P-2

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