The onset of deconfinement in nuclear collisions

We first consider the origin of colour deconfinement, comparing in I,articu lar spontaneous symmetry breaking and percolation. Next we specify the onse t of deconfinement in nuclear collisions through parton percolation, and wi th parameters determined at SPS energy, we give quantitative predictions fo r charmonium suppression at RHIC. Finally we show that the parton cascade m odel leads to similar predictions, starting from a microscopic description of the space-time evolution of the collision.