  We discuss the renormalized free energy of a heavy quark anti-quark pair in
the color singlet channel for quenched and full QCD at finite temperature. The
temperature and mass dependence, as well as its short distance behavior is
analyzed. Using the free energies we calculate the heavy quark potential and
entropy in quenched QCD. The asymptotic large distance behavior of the free
energy is used to define the non-perturbatively renormalized Polyakov loop
which is well behaved in the continuum limit. String breaking is studied in the
color singlet channel in 2-flavor QCD.
