Heavy quark bound states in a quark-gluon plasma

Bound states of heavy quarks have been considered as a sensitive probe of the quark-gluon plasma since the early days of ultra relativistic heavy ion experiments. However, the dynamics of heavy quarks in a plasma, and more particularly the possible formation of bound states and their evolution, constitute a complicated many-body problem whose many features are not  yet fully understood. In this talk, after a brief review of the experimental situation, I shall present recent  theoretical progress on these issues.