After the fall of the Santer Commission in 1999, the new college undertook an in-depth internal administrative reform under the political leadership of Romano Prodi and Neil Kinnock. One big chapter of this reform dealt with senior personnel policy. New procedures were implemented, merit was upgraded as the main criteria for senior appointments, and compulsory redeployment was introduced. Against this background, the research was conducted in order to assess the extent to which these new measures have changed the way senior appointments take place inside the Commission, particularly in terms of influence coming from national governments. By assessing several hundred appointments and redeployments of director generals, deputy director generals and directors - and through interviews with 37 top Commission officials - the thesis revealed what substantive and systemic changes have progressively taken place since the early years of the Prodi Commission, as compared to the pre-reform situation (i.e. Santer Commission). Principal-agent theory was used to frame the research and derive the main hypotheses on the possible development in the relation between EU member states and the Commission. Among the main overall findings of the research, the empirical assessment revealed that 1) the role played by nationality in senior Commission appointments has undoubtedly decreased with the implementation of the reform; 2) the role of member states in senior appointments has changed little from Santer to Prodi, due to the complementary finding that this role was already rather limited prior to the reform (a finding which runs against the mainstream literature on this issue); 3) mobility was a senior management tool that certainly helped the Commission to bring forward change to the administrative culture, but did not come to represent a tool used to resist member states’ pressures; and 4) unfit candidates have no longer a chance to be promoted to the upper echelons of the Commission administration.