  QCD at finite temperature and density is becoming increasingly important for
various experimental programmes, ranging from heavy ion physics to
astro-particle physics. The non-perturbative nature of non-abelian quantum
field theories at finite temperature leaves lattice QCD as the only tool by
which we may hope to come to reliable predictions from first principles. This
requires careful extrapolations to the thermodynamic, chiral and continuum
limits in order to eliminate systematic effects introduced by the
discretization procedure. After an introduction to lattice QCD at finite
temperature and density, its possibilities and current systematic limitations,
a review of present numerical results is given. In particular, plasma
properties such as the equation of state, screening masses, static quark free
energies and spectral functions are discussed, as well as the critical
temperature and the QCD phase structure at zero and finite density.
