The 3rd International Conference on Cloud Computing and Services Science, CLOSER 2013, focuses on the emerging area of Cloud Computing, inspired by some latest advances that concern the infrastructure, operations, and available services through the global network. Further, the conference considers as essential the link to Services Science, acknowledging the service-orientation in most current IT-driven collaborations. The conference is nevertheless not about the union of these two (already broad) fields, but about Cloud Computing where we are also interested in how Services Science can provide theory, methods and techniques to design, analyze, manage, market etc. Cloud Computing. Emerging Enterprise Technologies are profoundly changing the way we think of IT - from economics and efficiency to process and usage models. Many organizations look to the “externalized” IT systems and services as a potential cost-savings advantage by moving internally hosted IT services to external providers. Other organizations view the “external” IT as potential disaster recovery systems or as on-demand capacity to boost business continuity and customer service levels. We need to take a closer look, discerning what emerging enterprise technologies are and how they can catalyze creativity and produce a competitive advantage. There is hence a new wave of interest in 'Externalization of IT' - anything as a service (including Software as a Service, Infrastructure as a Service, Platform as a Service), On Demand delivery, outsourcing, and so on. This emerging facilitation and way of utilizing services through IT is what we are referring to as Cloud Computing. The four perspectives in which we are addressing the area of Cloud Computing in this conference are: (i) Fundamentals of Cloud Computing; (ii) Services Science foundations for Cloud Computing; (iii) Cloud Computing platforms and applications; (iv) Cloud Computing enabling technology.