Differentiated participation, uniform procedures: EU agencies in direct policy implementation

The European Union (EU) is characterised by a plethora of differentiated implementation practices. What brings about such differentiation, and how does this vary across policy fields? Drawing on theories of differentiated integration, we argue that the determinants of differentiated implementation occur at the intersection of postfunctional obstacles (politicisation) and functional pressures for joint implementation (interdependence between member states). We break down implementation along two dimensions, a territorial one referring to states’ discretion to participate in such activities, and a procedural one capturing the degree of uniformity in the organisation of implementation practices. We apply the resulting typology to the case of joint operations conducted by EU agencies alongside national authorities. We find that differentiated participation is a stable feature of joint operations in politicised fields; moreover, although there is a tendency to create uniform procedures over time and across policy fields, higher uniformity prevails in areas of symmetric interdependence.