  Heavy-quark production provides a sensitive probe of the gluon structure of
nucleons and its modication in nuclei. It is also a key probe of the hot-dense
matter created in heavy-ion collisions. We will discuss the physics issues
involved, as seen in quarkonia and open heavy-quark production, starting with
those observed in proton-proton collisions. Then cold nuclear matter effects on
heavy-quark production including shadowing, gluon saturation, energy loss and
absorption will be reviewed in the context of recent proton-nucleus and
deuteron-nucleus measurements. Next we survey the most recent measurements of
open-charm and J/Psi's in heavy-ion collisions at RHIC and their
interpretation. We discuss the high-pT suppression and flow of open charm in
terms of energy loss and thermalization and, for J/Psi, contrast explanations
in terms of screening in a deconfined medium vs. recombination models.
