Infrared-safe quantities at NLO in QCD

Using a general formalism based upon the subtraction method, I discuss the numerical evaluation of next-to-leading order QCD cross sections for the production of any number of jets in any type of hard collisions. I show how to implement the formalism in a computer code 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.