Operational psychology continues to expand at a rapid rate. Over the course of the last decade, it has emerged from relative obscurity and developed into an exciting, and somewhat controversial, professional subdiscipline within psychology. As the community of operational psychologists has increased and matured, it has reached a tipping point, creating the need for practice guidelines, training programs, and a greater emphasis on operationally relevant empirical research. The starting point for these developments is an integrative definition of operational psychology. In this article, we revisit previous definitions, relevant research literature, and recent developments in this specialty. We propose a definition that emphasizes consultation to an operational decision maker concerning issues of national security and defense.