[...] The discussion below is organized into four sections. The first reviews the powers of the Commission President. Comparison with heads of government at the national level brings out its weakness. The second examines how Commission Presidents before Barroso approached the office. It shows that his predecessors adopted one of five strategies, each defined by the type of resources mobilized. The third section focuses on the Barroso Presidency. It highlights the strength of Barroso's leadership and discusses what distinguishes the Barroso Presidency from previous presidencies. It then considers how the new style of leadership came about. The fourth section compares the advantages and disadvantages of a strong presidential leadership of the Commission, investigates the impact of the Barroso Presidency on the Commission, and considers whether the model is likely to endure. The conclusion summarizes the main arguments, reflects on the significance of the emergence of the new model, and suggests lines for future research. Two points of contextualization are necessary at the outset. The first is that paper is narrowly concerned with leadership of the Commission only - essentially the Commission President's relationship vis-à-vis the College and the Commission services - and that it investigates changes in the Commission Presidency as a political office, the leadership strategy and style of Commission Presidents, and the resources mobilized by its various incumbents. While it makes reference to studies that have examined leadership in a broader sense, such as Endo (1999), Grant (1994) and Ross (1995), the paper does not make wider claims about, for example, the Commission President in the context of leadership of the EU or Europe - or about the policy achievements of any particular Commission President (see, e.g., Tömmel 2013). The second point is that the analysis presented below falls within the interactionist school of leadership. It recognizes that leadership is the outcome of a combination of the incumbent's characteristics and the environment in which he or she operates. It also acknowledges that the mobilization of resources by an individual outside the organization may have implications for his or her standing inside it. In the case of the Commission President, the ability to perform effectively in the European Council or in the European Parliament is likely to have an impact on his or her authority within the Commission.