Commissioned amidst allegations of collusion between American Psychological Association officials and Central Intelligence Agency and Department of Defense officials involved in the enhanced interrogation programme, the July 2015 Hoffman Report documented a decade of collusion between American Psychological Association and Department of Defense officials in unethical national security interrogations. However, interrogation support is but one of numerous areas where psychologists are directly aiding military and intelligence operations, an area known as operational psychology. The ethical issues posed by the larger field of operational psychology have received little public discussion apart from apologia by operational psychologists themselves. To stimulate public review of operational psychology, leaders of the movement to remove psychologists from national security interrogations convened, in September 2015, a group of experts to work towards a consensus set of principles to guide future discussion. Participants included psychologists, physicians, and social scientists; military and intelligence professionals; and attorneys, ethicists, and human rights advocates. The discussion also drew upon years of dialogue between participants and military health and intelligence professionals. The workshop produced “The Brookline Principles on the Ethical Practice of Operational Psychology,” with implications for the profession of psychology and for civil society.