We report on a determination of the strong coupling constant
from a fit of QCD predictions for six event-shape variables, calculated at next-tonext-to-leading order (NNLO) and matched to resummation in the next-to-leadinglogarithmic approximation (NLLA). We use data collected by ALEPH at centre-ofmass energies between 91 and 206 GeV. We also investigate the role of hadronisation
corrections, using both Monte Carlo generator predictions and analytic models to parametrise non-perturbative power corrections
