The 6th Advanced Course in Theoretical Physics was held at the University of Cape Town, January 8-19, 1990. The topic of the course was "e;Phase Structure of Strongly Interacting Matter"e;. There were ten invited speakers from overseas, each having up to six hours in which to present his field of research to a relatively small audience of about 50 participants. This allowed for the presentation of a broad, coherent and pedagogical review of the present status of the field. In addition there were several one-hour presentations by local participants. The main emphasis of the course was on the study of the properties of high- density hot nuclear matter. This field is of particular interest because of the belief that a deconfined quark-gluon plasma could be created in such an environment when the temperature reaches about 200MeV. In the nuclear regime a so-called "e;liquid-to-gas"e; phase transition is expected at a temperature of approximately 10- 20MeV. Both of these topics received ample attention at the school. Owing the nature of the field, there exists much overlapping interest from both the nuclear physics and high-energy particle physics communities. It is hoped that these proceedings will contribute to building a bridge between the two groups.