  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.
