This book offers a comprehensive guide to ethical decision-making for practitioners of operational psychology working in national security and defense. The terrorist attacks of 9/11 led to the mass recruitment, training, and employment of psychologists to support national security, national defense, and public safety initiatives. The result was a confluence of advances in the field, alongside highly controversial missteps and calls for greater guidance. This book aims to improve practitioners’ ability to recognize ethical dilemmas before they arise, assess the risks they present, and respond to them in a manner characterized by thoughtful engagement and virtuous behavior. The work adopts an integrated approach, providing a holistic treatment of ethics and ethical decision-making. It begins with the establishment of a broad theoretical foundation of moral reasoning and ends with presentations of relevant rule-based codes, illustrative case studies, real-world contemporary issues, and practical solutions to common ethical problems. The book is unique in its comprehensive ethics case analysis of operational psychology, and ethical dilemmas are presented both by issue and by practitioner core competencies. As such, it enables readers to easily cross-reference ethical dilemmas by the nature of the dilemma and by its context (where it is most likely to occur). This book will be essential reading for psychologists working in national security, national defense, and public safety sectors and of much interest to students of ethics and ethical decision-making.