QCD studies at LEP I

The high hadronic event statistics collected at the Z energy (LEP I) allowed a good understanding of the QCD dynamics. The coupling constant \alpha_s has been measured with several methods giving a global average \alpha_s(M_Z) = 0.122 \pm 0.004. The flavour independence of \alpha_s has been tested obtaining \alpha_s^b/\alpha_s^{udsc} = 0.997 \pm 0.023. Quark-gluon jet differencies has been observed among which <n>_{gluon}/<n>_{quark} = 1.234 \pm 0.027. A big role has been plaied by the silicon vertex detectors.