This book constitutes the thoroughly refereed proceedings of the 5th International Conference on Cloud Computing and Services Science, CLOSER 2015, held in Lisbon, Portugal, in May 2015. The 14 revised full papers presented together with one invited paper were selected from 146 paper submissions. The papers focus on the following topics: cloud computing fundamentals; services science foundations for cloud computing; cloud computing platforms and applications; cloud computing enabling technologies; and mobile cloud computing services.