Saul Gass has been a leading contributor to the field of Operations Research for more than 50 years. He has been affiliated with the Robert H. Smith School of Business at the University of Maryland for more than 30 years. On February 25, 2006, "Operations Research in the 21st Century: A Symposium in Honor of Professor Saul Gass' 80th Birthday," was held on our campus. Opening remarks by Deans Howard Prank and Rudy Lamone were followed by talks by Alfred Blumstein, Karla Hoffman, Richard Larson, Christoph Witzgall, Thomas Magnanti, Rakesh Vohra, and Bruce Golden. The celebration continued into the evening with dinner in the Executive Din­ ing Room of Van Munching Hall, followed by numerous toasts to Saul. It was a special day for all of us who were in attendance, but it was especially memorable for Saul and his family. This Festschrift companion to the Symposium includes articles from each of the Symposium distinguished speakers plus 16 other articles from friends, colleagues, and several of Saul's former students. The book is divided into three sections. The first section comprises eight articles focusing on the field of Operations Research from a historical or professional perspective. The second section contains nine articles whose theme is optimization and heuristic search, while the third section includes six articles in the general area of modeling and decision making. Collectively, these articles pay tribute to Saul Gass' major interests in the field of Operations Research.