A general approach to jet cross sections in QCD

I illustrate a general formalism based upon the subtraction method for the calculation of next-to-leading order QCD cross sections for any number of jets in any type of hard collisions. I discuss the implementation of this formalism in a numerical program which generates partonic kinematical configurations with an appropriate weight, thus allowing the definition of arbitrary jet algorithms and cuts matching the experimental setup at the last step of the computation. I present results obtained with computer codes which calculate one-jet and two-jet inclusive quantities in photon-hadron and hadron-hadron collisions.