The Association of Southeast Asian Nations (ASEAN) established its first human rights body in 2009: the ASEAN Intergovernmental Commission on Human Rights (AICHR). Given the traditional interpretations of ASEAN norms such as sovereignty, non-interference, equality and independence, this was a curious development. In particular, the norms of sovereignty and in the internal affairs of one another have been central to the code of conduct among ASEAN member states since the organization was established in 1967, and are reiterated in ASEAN agreements and declarations. (1) The non-interference norm means that domestic governance issues, including member states' human rights records, traditionally have been off the table in official ASEAN dialogue. It also means that member governments have refrained from publicly criticizing each other's actions. Moreover, only five of the ten member states have national human rights bodies (with varying mandates and degrees of independence from their respective governments). (2) Why, then, did ASEAN create a regional human rights body? The references to human rights and the creation of a human rights body raise the question of whether traditional interpretations of ASEAN norms are under challenge. The case study also raises a more fundamental question: why and how do norms emerge and evolve among states in a regional institutional context? This puzzle has implications for the study of regional organizations. ASEAN is a particularly interesting case in this regard because of its environment of contestation. Norms are dynamic and evolve over time, and there may be tensions between norms in a regional institutional environment. Moreover, member states have diverse understandings of ASEAN norms. This article takes a consciously Constructivist approach in its recognition of ideational factors and sociological dynamics in international relations. This article traces the negotiations leading to the adoption of the ASEAN Charter, focusing on the processes through which ten member states with significantly diverse identities, interests and practices accepted references to human rights as principles and purposes of ASEAN, and agreed to create a human rights body. After a period of debate, negotiation and drafting from January to November 2007, ASEAN member states agreed to make a normative about human rights in the Charter. In this article, a statement represents rhetorical adoption of a norm in an official text, even if that norm has not been internalized. In contrast, the term is used to denote the common understanding of a norm: a standard of appropriate behaviour for actors with a given identity. (3) The article traces the processes through which ideas are initially proposed and advanced, and eventually emerge in agreed-upon text. As such, it provides a case study of the emergence and evolution of norms in a regional institutional context. This article argues that regional norms are shaped by competing perceptions of legitimacy. Legitimacy refers here to the social judgements of an entity as appropriate, proper or desirable, within a particular institutional environment. Member states' interpretations of the legitimacy of ASEAN and its norms as perceived by those outside the region--external regional legitimacy--were crucial in shaping the decision to establish a regional human rights body. In particular, the international outrage over the Myanmar regime's crackdown on protesting monks in September 2007 brought ASEAN's legitimacy concerns into sharp relief. ASEAN officials were concerned about the impact of this event, and of Myanmar's membership generally, on ASEAN's reputation and credibility. They believed that creating a human rights body was an important mechanism to improve the legitimacy of ASEAN and its norms, as perceived by extra-regional actors. Thus, member states--even those who generally resist increased interference in internal affairs, and those with poor human rights records--accepted the need to adopt references in the Charter to provide a role for ASEAN vis-a-vis human rights. …