The European Energy Policy aims at achieving three core objectives: sustainability, competitiveness and security of supply. The achievement of these objectives requires a profound transformation of the energy system that will imply a huge and coordinated effort across several areas. This effort must rely on a sound analysis of different policy approaches, regulatory measures and technological choices. ICT must play a key role as one of the enablers of the energy system transformation, but also as an enabler of new advances in the modeling, analysis and governance of the system.The energy system is a clear example of a large-scale sociotechnical system composed by a myriad of heterogeneous elements working at different scales. The complex behaviour that emerges from these interactions drives classical modeling methods to their limits. Complex Systems Science is emerging as a discipline capable of offering new methods for a realistic, robust and flexible modeling of such kind of systems. New tools such as Agent-Based Simulation or Complex Networks have led to valuable results in several fields, but their application to the energy system still faces a number of open issues that require further research.ComplexEnergy is a support action whose purpose is to bridge the ICT, Energy and Complex Systems research communities in order to:- build the foundations for a new, EC-scale, interdisciplinary research community able to formulate innovative approaches to energy system modeling, design and governance;- carry out a well-defined and systematic consultation of these three research communities, as well as of policy makers and other relevant stakeholders, with the aim to identify the main strategic areas, the emerging research avenues and the major research challenges at the junction of ICT, Energy and Complex Systems; and- define a roadmap for the development of these research trends, including recommendations on research topics for FP7 calls in 2011 and beyond.