If there is – as it has now been largely acknowledged – a general trend towards setting up EU-level regulatory agents in order to palliate the lack of EU regulatory capacity, how can we explain that the type of regulatory agent created varies between sectors and changes over time? Focusing on the expert committees, regulatory networks, and EU regulatory agencies, this paper makes two conjectures. It first argues, in a functional institutionalist approach, that the type of regulatory agent depends on the distribution of implementing competences between the member states and the Commission. While national competences, spurring a need for coordination, would lead to the establishment of regulatory networks (coordination pattern), a significant delegation of competences to the Commission would lead to a lack of expertise and resources, which would be filled through the creation of expert committees (expertise pattern). Secondly, the paper conjectures that the subsequent replacement of regulatory networks and expert committees by EU regulatory agencies is best explained by policymakers’ willingness to improve the effectiveness and quality of EU regulation. Two in-depth case studies on the regulation of food safety and electricity confirm the plausibility of the conjectures by providing good illustrations of the causal mechanisms at play in the expertise and coordination patterns, respectively. Besides taking a first step towards identifying the determinants of the many faces of the EU regulatory space, this paper underlines the need to refine the conceptualisation of functional pressure and colouring the study of institutional choice, otherwise dominated by distributional and institutional factors, with a revamped functional approach.