Thoroughly revised and updated, this new edition develops the basic formalism and theoretical techniques for studying relativistic field theory at finite temperature and density. It starts with the path-integral representation of the partition function and then proceeds to develop diagrammatic perturbation techniques. The standard model is discussed, along with the nature of the phase transitions in strongly interacting systems and applications to relativistic heavy ion collisions, dense stellar objects, and the early universe. First Edition Hb (1989): 0-521-35155-3 First Edition Pb (1994): 0-521-44945-6