This book constitutes the thoroughly refereed post-conference proceedings of the First International Workshop on Energy Efficient Data Centers (E2DC 2012) held in Madrid, Spain, in May 2012. The 13 revised full papers presented were carefully selected from 32 submissions. The papers cover topics from information and communication technologies of green data centers to business models and GreenSLA solutions. The first section presents contributions in form of position and short papers, related to various European projects. The other two sections comprise papers with more in-depth technical details. The topics covered include energy-efficient data center management and service delivery as well as energy monitoring and optimization techniques for data centers.