The contribution of computer simulation studies to our understanding of proper ties of a wide range of condensed-matter systems is now well established. The Center for Simulational Physics has been hosting annual workshops with the in tent of bringing together some of the experienced practitioners in the field, as well as relative newcomers in the field, to provide a forum for the exchange of ideas and recent results. This year’s workshop, the fourth in the series, was held at the University of Georgia, February 18-22, 1991. These proceedings are a record of the workshop and are published with the goal of timely dissemination of the papers to a wider audience. The proceedings are divided into three parts. The first part contains invited papers which deal with simulational studies of classical systems and includes an introduction to some new simulation techniques and special purpose comput ers as well. A separate section of the proceedings is devoted to invited papers on quantum systems including new results for strongly correlated electron and quantum spin models believed to be important for the description of high-T c superconductors. The contributed presentations comprise the final chapter.