  The purpose of this paper is to give a short microlocal proof of the
meromorphic continuation of the Ruelle zeta function for C^\infty Anosov flows.
More general results have been recently proved by Giulietti-Liverani-Pollicott
[arXiv:1203.0904] but our approach is different and is based on the study of
the generator on the flow as a semiclassical differential operator.
