2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/48146Within the next few years experiments at RHIC and the LHC will seek to create in the laboratory a quark-gluon plasma, the phase of matter through which the Universe passed very early in its life. It is believed that the plasma will survive long enough to reach thermal equilibrium. I give an introduction to the formalism of thermal field theory, the combination of statistical mechanics and quantum field theory needed to describe the plasma in thermal equilibrium, in a way that tries to keep close to the physics it describes.14 pages, plain tex. Lectures given in August 1998 at the University of Regensburg, based on a course given in February 1997 at the IX Jorge Andre Swieca Summer School, Campos do Jordao, BrazilHigh Energy Physics - PhenomenologyHigh Energy Physics - Theorytext