  A review of measurements of $\alpha_s$ is given, representing the status of
April 2004. The results prove the energy dependence of $\alpha_s$ and are in
excellent agreement with the expectations of Quantum Chromodynamics, QCD.
Evolving all results to the rest energy of the $Z^0$ boson, the world average
of $\alpha_s(M_Z)$ is determined from measurements which are based on QCD
calculations in complete NNLO perturbation theory, giving $\alpha_s(M_Z) =
0.1182 \pm 0.0027 .$
