Perturbative QCD at finite temperature and density

This is a comprehensive review on the perturbative hot QCD including the recent developments. The main body of the review is concentrated upon dealing with physical quantities like reaction rates. Contents: \S1. Introduction, \S2. Perturbative thermal field theory: Feynman rules, \S3. Reaction-rate formula, \S4. Hard-thermal-loop resummation scheme in hot QCD, \S5. Effective action, \S6. Hard modes with $|P^2| \leq O (g^2 T^2)$, \S7. Application to the computation of physical quantities, \S8. Beyond the hard-thermal-loop resummation scheme, \S9. Conclusions.