The basic methods of perturbative quantum chromodynamics are introduced and developed through an analysis of short- and long-time dependence in time-ordered perturbation theory for quantum fields. Jet cross sections are shown to be dominated by short times, and hence to be infrared safe. Next, the factorization of short- and long-time dependence for inclusive hard cross sections involving hadrons in the initial state is discussed. The basic results of the parton model, the evolution of deeply inelastic scattering structure functions and the resummation of Sudakov corrections in e+e− annihilation are derived from factorization. The lectures conclude with a brief account of the relation between high orders in perturbation theory and power corrections in e+e− annihilation.