This book presents recent developments in the functionality of generation unit commitment (UC) models and algorithms for solving those models. These developments, the subject of a September 1999 workshop, are driven by institutional changes that increase the importance of efficient and market responsive operation. We illustrate these developments by demonstrating the use of mixed integer programming (MIP) to solve a UC problem. The dramatically lower solution times of modem MIP software indicates that it is now a practical algorithm for UC. Participants in the workshop also prioritized the features that need to be considered by UC models, along with topics for research and development. Among the highest research priorities are: market simulation; bid selection; reliability and reserve constraints; and fair processes for choosing from alternative near-optimal solutions. The chapter closes with an overview of the contributions of the other chapters.