Calculation of QCD jet cross sections at next-to-leading order

A general method for calculating \NLO cross sections in perturbative QCD is presented. The algorithm is worked out for calculating $N$-jet cross sections in hadron-hadron collisions. The generalization of the scheme to performing caclulations for other QCD process, such as electron-positron annihilation or in deep inelastic scattering is also straightforward. As an illustration several three-jet cross section distributions in electron-positron annihilation, calculated using the algorithm, are presented.