Important progress in understanding the behavior of hadronic matter at high
density has been achieved recently, by adapting the techniques of condensed
matter theory. At asymptotic densities, the combination of asymptotic freedom
and BCS theory make a rigorous analysis possible. New phases of matter with
remarkable properties are predicted. They provide a theoretical laboratory
within which chiral symmetry breaking and confinement can be studied at weak
coupling. They may also play a role in the description of neutron star
interiors. We discuss the phase diagram of QCD as a function of temperature and
density, and close with a look at possible astrophysical signatures.Comment: 91 pages. latex with sprocl.sty. 6 eps figures. To appear as Chapter
35 in the Festschrift in honor of B. L. Ioffe, "At the Frontier of Particle
Physics / Handbook of QCD", M. Shifman, ed., (World Scientific). v2:
References correcte
