  We present results obtained from a study of the structure of hadronic events
recorded by the L3 detector at various centre-of-mass energies. The
distributions of event shape variables and the energy dependence of their mean
values are measured from 30GeV to 189GeV and compared with various QCD models.
The energy dependence of the moments of event shape variables is used to test a
power law ansatz for the non-perturbative component. We obtain a universal
value of the non-perturbative parameter alpha_0 = 0.537 +/- 0.073. From a
comparison with resummed O(alpha_s^2) QCD calculations, we determine the strong
coupling constant at each of the selected energies. The measurements
demonstrate the running of alpha_s as expected in QCD with a value of
alpha_s(m_Z) = 0.1215 +/- 0.0012 (exp) +/- 0.0061 (th).
