We extend a huge thank you to Dr. W. David Kelton who made significant contributions as co-author to the first five editions of this book and to Dr. Alexander Verbraeck, who was co-author of the first edition. Dr. C. Dennis Pegden provided significant contributions to the scheduling chapter and on the topic of AI and simulation. Many other people helped us get to this point. The Simio LLC technical staff — Cory Crooks, Glenn Drake, Glen Wirth, Dave Takus, Renee Thiesing, Katie Prochaska, and Christine Watson — were great in helping us understand the features, find the best way to describe and illustrate them, and even provided proofreading and help with the case studies. Jan Burket and Alex Molnar helped us with proofreading. Eric Howard, Erica Hedderick, and Molly Arthur of Simio LLC provided great support in helping get the word out and working with early adopters. Chris Havelka helped with the conversion to online format in the sixth edition. From Auburn University, Chris Bevelle and Josh Kendrick worked on the new introductory case studies, James Christakos and Yingde Li worked on material for the first edition, Ashkan Negahban provided much support during his years as a PhD student, and Grant Romine and Samira Shirzaei provided assistance with the fifth edition. While we appreciate the participation of all of the early adopters, we’d like to give special thanks to Jim Grayson, Gary Kochenberger, Deb Medeiros, Barry Nelson, Leonard Perry, and Laurel Travis (and her students at Virginia Tech) for providing feedback to help us improve.