Magnetic and electric Z(N) symmetry in hot QCD

Consider QCD with only adjoint matter-or more generally centergroup-neutral matter, in 2+1 and 3+1 dimensions with gauge group SU(N). It has an electr ic Z(N) symmetry, which is unbroken at low temperatures. At high temperatur e this symmetry is spontaneously broken. There is also a magnetic Z(N) symm etry, broken at low temperature, as pointed out long ago by 't Hooft. In th is talk we explain why the 't Hooft loop has area behaviour in the plasma p hase, and that the magnetic Z(N) is restored at high T.