  The current status of tests of the theory of strong interactions, Quantum
Chromo Dynamics (QCD), with data from hadron production in e^+e^- annihilation
experiments is reviewed. The LEP experiments ALEPH, DELPHI, L3 and OPAL have
published many analyses with data recorded on the Z^0 resonance at sqrt(s)=91.2
GeV and above up to sqrt(s)>200 GeV. There are also results from SLD at
sqrt(s)=91.2 GeV and from reanalysis of data recorded by the JADE experiment at
14<sqrt(s)<44 GeV. The results of studies of jet and event shape observables,
of particle production and of quark gluon jet differences are compared with
predictions by perturbative QCD calculations. Determinations of the strong
coupling constant alpha_S(M_Z) from jet and event shape observables, scaling
violation and fragmentation functions, inclusive observables from Z^0 decays,
hadronic tau decays and hadron production in low energy e^+e^- annihilation are
discussed. Updates of the measurements are performed where new data or improved
calculations have become available. Finally, investigations of the gauge
structure of QCD are summarised.
