Determination of alpha_s(M_Z²) from hadronic event shape observables in e+e- annihilation

The determination of alpha_s(M_Z^2) using O(alpha_s^2) calculations of hadronic event observables in e+e- annihilation is reviewed. The large scatter among alpha_s(M_Z^2) values determined from different observables may be interpreted as arising from the effect of uncalculated higher-order contributions. The application of `optimised' perturbation theory and Pade approximants in an attempt to reduce this effect is discussed.