Enforcing EU policies: why do EU legislators prefer new networks of national authorities and not existing EU agencies?

Networks of national authorities are often mandated to help enforce EU policies, but receive less scholarly attention than EU agencies. This article examines two networks in the policy areas of medical devices and aviation incident investigation. These are puzzling cases, as two EU agencies already existed in similar policy areas: the European Medicines Agency (EMA) and the European Aviation Safety Authority (EASA). Why did EU legislators mandate new networks of national authorities, and not existing EU agencies? The article argues that national authorities' experts held a central position in the decision-making process and have considerably influenced the decision not to mandate the EMA and the EASA. The article also refines a common assumption about the Commission, and argues that it seems less keen to establish new EU agencies if these already exist in largely similar policy areas. The article's case studies rely on 24 interviews and an analysis of primary and secondary documentation. [ABSTRACT FROM AUTHOR]