This thesis explores the advocacy strategies and influence of interest groups in EU foreign policy. It examines in particular the impact of institutional factors on the strategies and lobbying outcomes. Conceptually, it contributes to the literature on interest groups and lobbying in the EU and to the study of non-state actor participation in international organisations. Conceptualising EU foreign policy as multi-level and multi-pillar, the study inquires into the relationship between policy regime (ranging from the Community method to the intergovernmental method, as these predominate in different areas of EU external relations) and the degree and type of interest group influence. To this end the thesis compares three examples of EU foreign policy: visa liberalisation towards the Eastern neighbours; sanctions towards Belarus; and CSDP missions in Georgia and Palestine. The research reveals that interest groups engage in multi-level lobbying even in those policy areas that are ruled by the intergovernmental method. Intergovernmentalism limits formal access to policymakers, but groups and policymakers build channels for informal access. To some extent contrary to the predications of established theories, this allows interest groups to exert some degree of influence even on policy dossiers in which intergovernmental arrangements prevail. In such policy domains, groups opposing change do not always succeed, despite the veto opportunities that intergovernmentalism provides. While this is a significant finding, the thesis also notes how interest group influence is most commonly exerted upon relatively technical issues and at later stages of the policy cycle. Moreover, the study emphasises that institutional structures are not the only relevant factor in explaining group influence. Group-level characteristics, including material resources, condition groups’ ability to adapt to complex decision-making in EU foreign policy. The thesis concludes that a combination of factors is required to capture the influence of interest groups over EU foreign policy.