Climate change is increasingly acknowledged as a threat to states and societies, and several international organizations are now seeking to respond to climate-related security risks. The EU’s comprehensive approach to security suggests that the Union is particularly well-suited to respond to such risks, but the EU has not yet developed a coherent policy. This article addresses the gap between discourse and policy outcomes by exploring how practice shapes EU climate security policy. It provides unique insights based on practitioners’ accounts of the work being done in the European Union External Action Service to align various EU foreign policy tools and instruments in order to address climate-related security risks. A key finding is that a community of practice is emerging on climate security in the EU, but it is characterized by overlapping and conflicting practices relating to climate diplomacy, development, and security and defence.