Hadronic event structure, power corrections and the strong coupling at LEP

Infrared and collinear events shapes are suited to directly probe properties of hard QCD. They are traditionally used to measure the strong coupling and to test the gauge structure of QCD. Perturbative predictions exist in several variations all of which depend on the renormalisation scheme leading to large theoretical uncertainties in the determination of $alph{a}_s$. To overcome this dominating error more and more schemes for setting the renormalisation scale are investigated. The application of RGI perturbation theory shows an incredible small spread of ${\alpha }_s$ indicating a reduced uncertainty and allows a measurement of the $\beta$-function directly from mean values.