Tobias Lenz is post-doctoral fellow in a multi-year research project on the ‘Causes and Consequences of Multilevel Governance’, directed by Liesbet Hooghe and Gary Marks at the Free University of Amsterdam, the Netherlands. His research deals with regional organizations in a comparative perspective and the role of diffusion processes, especially from the EU. This piece draws heavily on two recent publications: ‘EU normative power and regionalism: ideational diffusion and its limits’, Cooperation and Conflict (Vol. 48, No. 2), and ‘Does regionalism diffuse? A new research agenda for the study of regional organizations’, Journal of European Public Policy (Vol. 20, No. 4, co-authored with Anja Jetschke). Tobias holds a D.Phil in International Relations from Oxford University, United Kingdom.