  Heavy quarkonia production is expected to be sensitive to the formation of a
quark gluon plasma (QGP). It was (and still is with ongoing data analyses)
extensively studied at the CERN SPS, at collision energy $\sqrt{s_{NN}}$ of the
order of 20 GeV. An anomalous suppression was clearly observed. The PHENIX
experiment at RHIC has presented preliminary results that exhibit a similar
amount of $J/\psi$ suppression, at ten times higher collision energy. I review
the results obtained at both facilities. While interpreting and comparing them,
the importance of understanding normal nuclear effects is emphasized. A new
method to derive a reference for Au+Au collisions from the centrality
dependence of d+Au measurements at RHIC is exposed.
