Determination of alpha_s(M_Z^2) 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.