  Jet cross sections in deep-inelastic scattering over a wide region of phase
space have been measured at HERA. These cross section measurements provide a
thorough test of the implementation of Quantum Chromodynamics in
next-to-leading order (NLO) calculations. They also provide the opportunity to
test the consistency of the gluon distribution in the proton as extracted from
(mainly) inclusive DIS measurements. Comparison of the cross sections with NLO
enables accurate extractions of the strong coupling constant, $\alpha_s$, to be
made, several of which are reported here.
