Ethical issues are at the heart of planning. Thus, planning theory has long displayed an interest in debating both the ethical justification for planning and how the activity of planning can be rendered more ethically sensitive. However, comparatively little attention has been shown to how the very constitution of the planner as a ‘moral subject’ may be ethically problematic for planning practice. This article addresses this lacuna through an engagement with the philosophy of Michel Foucault. In contrast to how his work is normally applied, this article accords with Foucault’s own direction that his later examination of ethics be used as a lens through which to read his earlier analysis of power and knowledge. Accordingly, the article first outlines Foucault’s innovative reinterpretation of how power and knowledge operate in society before setting this within his novel reconception of ethics. This theoretical exposition is then employed to interpret the material drawn from in-depth qualitative interviews with 20 planning officers working in a range of different contexts. The article subsequently employs Foucault’s ethically informed reading of power and knowledge to identify ethical issues arising from the approaches used by practitioners to justify their planning activities. The article concludes by suggesting how such issues can be resolved.