  Results from the study of jets in hadronic final states produced in e+e-
annihilation at sqrt(s)=14 to 209 GeV are discussed. Precise measurements of
the strong coupling alpha_S at many points of sqrt(s) provide convincing
evidence for the running of alpha_S as expected by QCD. Several measurements of
the running b-quark mass m_b(M_Z) are combined yielding
m_b(M_Z)=(2.92+-0.03(stat.)+-0.31(syst.)) GeV and compared with low energy
results. Strong evidence for the running of the b-quark mass is found.
Experimental investigations of the gauge structure of QCD are reviewed and then
combined with the results for the colour factors C_A=2.89+-0.01(stat.)+-
0.21(syst.) and C_F=1.30+-0.01(stat.)+-0.09(syst.) and correlation coefficient
rho=0.82. The uncertainties on the colour factors are below 10% and the
agreement with the QCD expectation C_A=3 and C_F=4/3 is excellent.
