Quarkonium production in ultra-relativistic nuclear collisions: suppression versus enhancement

After a brief review of the various scenarios for quarkonium production in ultra-relativistic nucleus-nucleus collisions, we focus on the ingredients and assumptions underlying the statistical hadronization model. We then confront model predictions for J/psi phase space distributions with the most recent data from the RHIC accelerator. Analysis of the rapidity dependence of the J/psi nuclear modification factor yields first evidence for the production of J/psi mesons at the phase boundary. We conclude with predictions for charmonium production at the LHC.