First, the chapter examines the importance of ethics to investigative practice and argues that law, statements of rights, and rules of procedure are not sufficient in themselves to ensure good professional conduct. Second, it analyzes the moral dilemmas that face investigators, including those that derive from conflicting loyalties and competing value systems. Third, the chapter examines the corrosive effect of corrupt investigations on society, on the legitimacy and effectiveness of investigating organizations, and on individual investigators. Fourth, the chapter argues that effective investigators must demonstrate a range of technical and ethical virtues. In addition to being technically competent, investigators should have a strong ethical conception of investigation. Investigators and those who supervise them must manage ethical issues, just as they manage other aspects of investigation. A balanced mixture of personal commitment, ethical audit, monitoring, team management, and career development should promote ethical standards and behavior in criminal investigations. 2 figures, 1 table, 15 notes, and 47 references