Larry B. Rainey, PhD, is Founder and Senior Partner at Integrity Systems and Solutions, LLC, a consulting firm that specializes in modeling and simulation within missile defense and space operations domains. With more than 20 years of systems engineering experience, Dr. Rainey has also worked for the Missile Defense Agency and other U.S. Department of Defense organizations that address system of systems challenges. He has also been a visiting assistant professor of systems engineering at the Air Force Institute of Technology at Wright-Patterson Air Force Base Ohio and an assistant professor of systems engineering at the Colorado Technical University in Colorado Springs, Colorado. Andreas Tolk, PhD, is Chief Scientist of SimIS Inc., which provides modeling and simulation services, enterprise architecture knowledge, and integration solutions to its customers. Dr. Tolk is also Adjunct Professor in the Department of Engineering Management and Systems Engineering at Old Dominion University, as well as the author of Engineering Principles of Combat Modeling and Distributed Simulation, which is published by Wiley.