QCD results from the study of hadronicZ-decays

The high statistics data collected from hadronic Z -decays have lead to remarkable progress in the understanding of the dynamics of strong interactions. In addition to precision measurements of the strong coupling constant, the colour factors defining the gauge structure of QCD were determined with large accuracy. They are found to agree with the expectation for an unbroken SU(3) symmetry, thus establishing unambiguously the non-abelian nature of QCD. Higher order effects in many cases are known to next-to-leading logarithmic precision. Coherence effects as predicted in the framework of the modified leading-log approximation and local parton-hadron duality are experimentally well established. Studies of the hadronization process favour a chain-like production mechanism which bridges the gap between perturbative QCD as described by coherent parton shower models and the final state hadrons.