This article examines the policy transfer from the United Nations (UN) to the Association of Southeast Asian Nations (ASEAN) in the case of trafficking in persons (TIP). It presents pioneering empirical research that analyzes the processes and mechanisms of policy transfer between the UN and a regional organization. Institutional collective action and regime complex theories in international relations are used to complement the existing state-centric policy transfer framework. We argue that the UN-ASEAN policy transfer in TIP is characterized by a two-step process, starting with transfer from the UN to the ASEAN member states, followed by synthesis at the regional level. The consensus-based decision-making approach in ASEAN restricts transfer outcomes to a common low base of national preferences, which is the lowest common denominator. The ability of stakeholders in the TIP field to steer lesson drawing, emulation and coercive transfer at both the national and regional levels allows them to influence the lowest common denominator. At the same time, policy transfer to ASEAN is shaped by “forum-shopping” by the ASEAN member states and other stakeholders within the TIP regime complex, based on the comparative advantage between ASEAN and other cooperation mechanisms in solving TIP-related issues.