  High energy quarks and gluons play essential roles in the tomographic study
of relativistic heavy-ion collisions and of the quark-gluon plasma. They
interact with the traversed dense matter through elastic and inelastic
collisions, and lose some of their initial energy in the process. Experimental
observables for jet modification include single inclusive hadron production,
hadron emission opposite to a triggered hadron or photon, and full jet
observables. Here a brief review of parton energy loss and jet quenching in
high energy nucleus-nucleus collisions is presented.
