  A complex compact surface which carries an automorphism of positive
topological entropy has been proved by Cantat to be either a torus, a K3
surface, an Enriques surface or a rational surface. Automorphisms of rational
surfaces are quite mysterious and have been recently the object of intensive
studies. In this paper, we construct several new examples of automorphisms of
rational surfaces with positive topological entropy. We also explain how to
define and to count parameters in families of birational maps of the complex
projective plane and in families of rational surfaces.
