  We present results on heavy quark free energies in 2-flavour QCD. The
temperature dependence of the interaction between static quark anti-quark pairs
will be analyzed in terms of temperature dependent screening radii, which give
a first estimate on the medium modification of (heavy quark) bound states in
the quark gluon plasma. Comparing those radii to the (zero temperature) mean
squared charge radii of cha rmonium states indicates that the $J/\psi$ may
survive the phase transition as a bound state, while $\chi_c$ and $\psi'$ are
expected to show significant thermal modifications at temperatures close to the
transition. Furthermore we will analyze the relation between heavy quark free
energies, entropy contributions and internal energy and discuss their relation
to potential models used to analyze the melting of heavy quark bound states
above the deconfinement temperature. Results of different groups and various
potential models for bound states in the deconfined phase of QCD are compared.
