Scholars from a variety of perspectives stress the importance of norm clarity and precision for the successful establishment, institutionalization and internalization of norms. Norm ambiguity is commonly thought to be an impediment to norm construction and compliance. In this chapter, we argue that norm ambiguity can actually be crucial for facilitating consensus, flexibility and compliance. We identify conditions under which norm ambiguity can be constructive and suggest that consensus around a norm can sometimes best emerge when the norm is initially articulated in ambiguous and flexible terms and then incrementally adjusted over time through a process that we call the “norm feedback loop.” We then show how ambiguity has facilitated the development of the Responsibility to Protect (R2P) norm, tracing Rwanda-era debates over humanitarian intervention, Iraq-era backlash over interventionist abuses and Libya-era norm implementation.