Climate change mitigation and the imperative of a new sustainable energy paradigm are among the greatest challenges facing the world today, and they are high on the priority list of policy makers as well as within the scientific community. In this context significant efforts are being made in the design and implementation of energy and carbon mitigation policies at both European and national level. Evidence of this can be seen in the recent adoption by the EU of an integrated climate and energy policy that setts ambitious binding targets to be achieved by 2020 – known as the 20-20-20 targets of the EU Climate and Energy Package. Undoubtedly, the cost of these policies can be substantially reduced if a comprehensive impact assessment is made of the most efficient and cost-effective policy measures and technological options. Policy impact assessment therefore plays an important role in supporting the energy and climate decision-making process.