QCD Predictions for the Tau Hadronic Width: Determination of   alpha_s(M_\tau^2)
  The total $\tau$ hadronic width can be accurately calculated using analyticity and the operator product expansion. The theoretical analysis of this observable is updated to include all available perturbative and non-perturbative corrections. The experimental determination of $\alpha_s(M_\tau^2)$ and its actual uncertainties are discussed. 
A. Pich