  We first consider the origin of colour deconfinement, comparing in particular
spontaneous symmetry breaking and percolation. Next we specify the onset of
deconfinement in nuclear collisions through parton percolation, and with
parameters determined at SPS energy, we give quantitative predictions for
charmonium suppression at RHIC. Finally we show that the parton cascade model
leads to similar predictions, starting from a microscopic description of the
space-time evolution of the collision.
