How can codes of ethics acquire legitimacy—that is, how can they lay down obligations that will be seen by their subjects as morally binding? There are many answers to this question, reflecting the fact that moral agents have a host of different bases on which they may acknowledge code duties as ethically binding—or, alternatively, may reject those duties as morally irrelevant or actively corrupt. Drawing on a wide literature on legitimacy in other practical fields, this paper develops a multidimensional legitimacy framework, describing ten distinct sources of legitimacy. It illustrates how these sources can be seized, not only by the code’s content, but by opportunities presented in the main stages of code development, adoption and implementation. In so doing, it aims to provide practical resources for code developers and ethics reformers in organizations and industries to avoid critical missteps, and to maximize the impact and efficacy of their work.