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,
disuss several alternative explanations for the observed suppressions
and future prospects for distinguishing these different pictures.