Phases of QCD

In these lectures we provide an introduction to the phase structure of QCD. We begin with a brief discussion of QCD, the symmetries of QCD, and what we mean by a ``phase of QCD’'. In the main part of the lectures we discuss the phase diagram of QCD as a function of the temperature and the baryon density. We focus, in particular, on the high temperature plasma phase, the low temperature and low density nuclear phase, and the high density color superconducting phases.