Review on αs at LEP Review Article

To measure the strong coupling αs from event shape observables two ingredients are necessary: a perturbative prediction containing the dependence of observables on αs and a description of the hadronisation process to match the perturbative prediction with the hadronic data. As perturbative prediction O(αs2), NLLA and combined calculations are available. Beside the well known Monte-Carlo based models also analytical predictions, so called power corrections, exist to describee the hadronisation. Advantages and disadvantages of the different resulting methods for determining the strong coupling and its energy dependence will be discussed, the newest Delphi results will be presented, and an overview of the LEP results will be included.