This graduate textbook on optimal spacecraft trajectories demonstrates the theory and applications of using the minimum amount of propellant possible to reach a target destination. The author aims to produce the only comprehensive treatment of various aspects of this topic. It includes problems at the ends of the chapters and some of the appendices. But it is also suitable as a scholarly reference book as it includes recent research from the author and his colleagues. John Prussing, Professor Emeritus of Aerospace Engineering, University of Illinois John Prussing is Professor Emeritus of Aerospace Engineering at the University of Illnois at Urbana-Champaign. He holds a SB, SM and a ScD in 1967 in aerospace engineering all from MIT, and served as professor of aerospace engineering between 1969 and 2007, and continues to teach part time, including short courses at NASA. He has published over 80 articles and has authored/co-authored three books.