Jet are experimental signatures of quarks and gluons, which are produced in high energy processes such as the hard scattering of partons in pp collisions. Jets are objects reconstructed from the energy signal deposited in the calorimeters by the particles coming from the hadronization of quarks and gluons. Its production cross section is really large, it means they are many channels with jets in the fi nal state. Usually the energy deposited does not correspond to the initial energy carried by the particles, i.e. the response of the calorimeter is di fferent from one. This is due to calorimeter e ffects as dead material, non compensation and crack regions and to jet reconstruction eff ects such as out of cone energy. As a consequence the determination of the jet energy scale and the achievement of the optimal jet energy resolution have become of crucial importance.