Since the mid-2000s, a large number of EU agencies became involved in transferring the EU acquis to the European Neighbourhood Policy (ENP) countries. EU agencies focus on the institution-building and enhancing the capacity of third countries to bring their standards closer to the EU norms. At the same time, the extent of their involvement varies across policy fields, countries, and agencies: some EU agencies have strong institutionalised ties with third states, while others establish only ad hoc cooperation. Despite their active involvement in the neighbourhood, the external dimension of EU agencies remains largely unexplored; neither do we know what explains the variance in agencies' openness to participation of third countries. The paper fills this research gap by providing a systematic mapping of the transgovernmental outreach of EU agencies to the ENP countries across different policy domains and by explaining the variance across agencies and countries. It demonstrates that the external activities of EU agencies follow the sector-specific interdependency dynamics rather than the principal foreign policy goals of the EU. Such external cooperation patterns focus on the technocratic networks and the EU regulatory state building outside its borders that goes beyond the political boundaries of the regional integration endeavours of the EU.