High Temperature QCD

I discuss finite-temperature gauge theories as a framework to describe the quark-gluon plasma in the regime of high temperature where the gauge coupling is small, $g << 1$. I review recent progress in the understanding of the long-range physics, with emphasis on the collective phenomena and their consequences for the screening of the gauge interactions. I consider some of the infrared divergences of the perturbation theory, and discuss the physical mechanisms which remove these divergences.