The practice of providing psychological or behavioral science support to counterintelligence operations is relatively new, but actively evolving. Psychologists-some of whom refer to themselves as operational psychologists-provide assessments for, and consultations to, operators, case officers, service members, and others on psychological or behavioral issues relevant for planning, managing, or terminating elements of an operation and handling human assets. Specifically, they may conduct direct or indirect risk assessments, offer perspectives on source recruitment and handling, or support interrogations and other information-gathering activities. Counterintelligence's focal areas, currently, are counterespionage and counterterrorism. We describe how psychologists have provided value-added support to each of those Department of Defense missions.