The extensive literature on EU agencies mainly focuses on their establishment, organization, accountability and governance, as well their role in the harmonization of standards within the EU market. This significant literature does not pay adequate attention to the importance of the EU agencies’ behaviour as actors in policy promotion beyond the EU. Based on organization theory, this chapter aims to fill this gap and suggests that the EU agencies acquire organizational structural characteristics that enhance their role in the international arena with respect to the diffusion of policy ideas, principles, practices and policy models. The EU agencies develop their own capacity, interests and strategies; organize international arrangements; and become actors with the intention to diffuse policy ideas and standards beyond the EU. They do so through mechanisms of socialization, persuasion and learning. In order to operationalize this, the chapter investigates three decentralized agencies _ the European Environmental Agency, the European Medicines Agency and the European Food Safety Authority _ whose activities concentrate on the environment, health and food safety respectively. These agencies share a common interest in environmental and health quality within their risk assessment mandate. Variations in their organizational structural characteristics lead to differences in their behaviour and arrangements in the international arena.