  Quarkonia (J/Psi, Psi', Upsilon) production provides a sensitive probe of
gluon distributions and their modification in nuclei; and is a leading probe of
the hot-dense (deconfined) matter created in high-energy collisions of heavy
ions. I will discuss our current understanding of the modification of gluon
distributions in nuclei and other cold-nuclear-matter effects in the context of
recent p-p and p(d)-A quarkonia measurements. Then I will review the latest
results for nucleus-nucleus collisions from RHIC, and together with the
baseline results from d-A and p-p collisions, discuss several alternative
explanations for the observed suppressions and future prospects for
distinguishing these different pictures.
