This paper draws attention to the untapped potential of international law (IL) in understanding how security communities develop. It focuses, among others, on ‘transnational legal processes’ – a key overlooked variable – by highlighting what international relations (IR) theory can learn from IL. In so doing, the paper contributes to the literature in three ways. First, it proposes a definition and conceptualisation of regional norms in the study of security communities. Second, by pointing out legal and judicial factors that facilitate or hinder the legal internalisation of regional norms, and consequently affect the development of a security community, it suggests new important research questions that can help broaden the ontology of security communities and bring theoretical heft to the fundamental concept of peaceful change. Third, the paper discusses how and under what conditions regional norms contribute to maintaining reasonable expectations of peaceful change not only at the systemic or state elite level, but equally at the domestic societal level.