Tau Decays and $\alpha_s$

Abstract

The evolution of the determination of the strong coupling constant $\alpha_s$ from the leptonic branching ratios, the lifetime, and the invariant mass distributions of the hadronic final state of the $\tau$ lepton over the last two decades is briefly reviewed. The improvements in the latest ALEPH update are described in some detail. Currently this is one of the most precise $\alpha_s$ determinations. Together with the other determination at the $Z$ boson mass pole, they constitutes the most accurate test of the asymptotic freedom in QCD.