These proceedings provide a general summary of the theoretical and experimental results which have established QCD as the theory of the strong interactions in the past 20 years. The experimental status of this theory in e⁺e⁻ annihilation, deep inelastic lepton-nucleon scattering and hadron-hadron collisions is reviewed and the theoretical implications are critically discussed. In addition, our knowledge on the non-perturbative sector of QCD, based on lattice and sum rule approaches, is summarized.