This chapter shows the shifting entrepreneurial and cognitive leadership role of the Commission in promoting EU climate policies in three phases after the Kyoto Protocol, from the initiation of the EU ETS to the Energy Union. Leadership style has shifted from increasingly transformational to more transactional. The most important conditions for shifting leadership are internal and external, including the distribution of preferences among other EU policymakers, notably the member-states. The basic constitutional features empowering the Commission to develop climate policy have remained roughly stable throughout the three phases.