Institut de recherche sur les lois fondamentales de l'Univers

QCD is well-known to be a confining theory of quarks and gluons, but this is not true above the critical temperature, T_c (~ a trillion Celsius), and/or critical density, rho_c (~ a trillion tonnes per ml).

This "quark-gluon plasma" phase existed soon after the Big Bang, and is believed to exist in the cores of neutron stars. Recently this phase has been created in heavy ion collision experiments at Brookhaven, and will soon be studied by the ALICE detector in the LHC.

I will give an overview of the properties of this recently discovered phase, both from an experimental and theoretical viewpoint, concentrating on the results from lattice simulations.