Jet measurements with ATLAS

Jet cross sections have been measured in proton-proton collisions at different centre-of-mass energies. The data are compared to expectations based on next-to-leading order QCD calculations corrected for non-perturbative effects, as well as to next-to-leading order Monte Carlo predictions. The ratio of cross section measurements at different centre-of-mass energies allows to reduce experimental and/or theoretical uncertainties substantially. The data allow to constrain the gluon density. Measurements of multi-jet production and ratios of 3-to-2 jet rates are used to determine the strong coupling constant alpha_S.