Introduction Ever since the 1990s, the EU has aimed to play a leadership by example role in international climate negotiations, adding increasingly ambitious targets and policy instruments. In October 2014, the EU agreed to cut emissions of greenhouse gases (GHG) by 40 per cent in its member states between 1990 and 2030. The European Commission (henceforth: Commission) has played a shifting role in promoting this development. This chapter argues that the type and style of leadership exercised by the Commission have varied over time. ‘Leadership’ is here understood as an asymmetrical relationship of influence, where one actor guides or directs the behaviour of others towards a certain goal over a certain period of time (Underdal 1991: 140). Leadership is distinguished from the actions of an agent who actively engages in ordinary policy-making and bargaining (Malnes 1995). To qualify as leader, the Commission should have an independent influence on policymaking exceeding its formal role. The Commission has the potential to act as an entrepreneurial leader. Its resources may be used to formulate new policy ideas, mobilize support and craft consensus. Entrepreneurial leadership can be seen as a matter of finding the means and guiding others toward a common end. In climate policy, entrepreneurial leadership will require conviction, skill, energy and formal status. The scope for entrepreneurial leadership is likely to increase with uncertainties concerning decision makers’ preferences and possible solutions. A cognitive leader can shape and influence the preferences of other actors. Access to, and control over, the production and dissemination of relevant information is a key resource for cognitive leadership. A study of Commission expert groups indicates that the potential for cognitive leadership is particularly high in Directorate General (DG) Environment and DG Transport and Energy.1 Cognitive leadership exercised by the Commission presupposes asymmetrical knowledge vis-à-vis EU decision makers. Knowledge networks within the Commission and between the Commission and other actors can also take the form of an epistemic community with a shared set of beliefs in specific ‘diagnoses’ and ‘cures’. However, entrepreneurial and cognitive leadership are not mutually exclusive: they may prove particularly effective in combination.