This grant will support research in theoretical condensed matter physics to develop models and do calculations in order to describe the behavior of high temperature superconducting materials. This grant was selected from more than 260 proposals submitted in response to a solicitation for proposals in High Temperature Superconductivity in April, 1989. This research may provide valuable insight into the physical mechanisms responsible for this unusual behavior. The research is supported through the Condensed Matter Theory program with a significant contribution from the university.