The carbon footprint of data centers has dramatically increased over the past few years, making data centers one of the major contributors to energy consumption and climate change. For this reason, it is necessary to come up with efficient solutions – from both the hardware and software perspective – to tackle this issue, which is a real challenge for all experts working in the field of Green IT. Several European projects dealing with different aspects of this problem are currently active, and it is time to create synergies in order to make them yet more successful. The main goal of this workshop is to present and discuss European initiatives concerning energy-efficiency in data centers, including both infrastructure- and software-oriented solutions. Research papers in this area are welcome. The workshop will feature a keynote speach by André Rouyer (CG GDC), as well as several academic and industry papers related to the three organizing projects (All4Green, CoolEmAll and Eco2Clouds).