Perturbative QCD at High Temperature

Recent developments of perturbation theory at finite temperature based on effective field theory methods are reviewed. These methods allow the contributions from the different scales to be separated and the perturbative series to be reorganized. The construction of the effective field theory is shown in detail for phi^4 theory and QCD. It is applied to the evaluation of the free energy of QCD at order g^5 and the calculation of the g^6 term is outlined. Implications for the application of perturbative QCD to the quark-gluon plasma are also discussed.