The analysis of hadronic events in high-energy electron-positron annihilation often relies upon the clustering of individual hadrons into energetic jets. By solving our theory of strong interactions, Quantum Chromodynamics (QCD) perturbatively, we may make theoretical predictions for these multijet configurations. In this thesis we provide some calculational tools which are useful for evaluating terms in the perturbative series beyond leading order. These include a convenient method of dealing with one-loop integrals containing tensor denominators and universal factorization formulae for matrix elements where two particles are unresolved, which are relevant at the 2-loop (next-to-next-to-leading order) level. In particular we concentrate on the case of the next-to-leading order corrections to 4 jet production (and related processes) and apply . our techniques to obtain explicit results in electron-positron annihilation which are then compared with experimental data.