TTP04-30 Perturbative QCD and tau-decays

The current status of the higher order QCD corrections to the width of the tau is discussed. We report on the result of the first complete calculation of the quadratic quark mass correction to the correlator of the two currents relevant for the strangeness-changing semihadronic tau-decay rate (including its real part at the four-loop level. We discuss phenomenological implications for determination of m_s.