Precision QCD measurements at HERA: Jet production and αS determination

A review of recent high precision measurements of inclusive-jet, dijet and trijet production in deep-inelastic scattering and photoproduction at HERA is presented. The data are compared to NLO QCD prediction. The measurements are used to extract the value of the strong coupling αS (MZ). Also, the test of QCD evolution mechanisms using the azimuthal correlation between the most forward jet and the scattered positron is presented.