Experimental tests of asymptotic freedom

Quantum chromodynamics (QCD), the gauge field theory of strong interaction, has specific features, asymptotic freedom and confinement, which determine the behaviour of quarks and gluons in particle reactions at high and low energy scales. QCD predicts that the strong coupling strength αs decreases with increasing energy or momentum transfer, and vanishes at asymptotically high energies. In this review, the history and status of experimental tests of asymptotic freedom are summarized. The world summary of measurements of αs is updated, leading to an unambiguous verification of the running of αs and of asymptotic freedom, in excellent agreement with the predictions of QCD. Averaging a set of measurements balanced between different particle processes and the available energy range, results in a new and improved world average of αs(MZ0)=0.1189±0.0010.