In this book, we propose a new approach to achieve the notion of HPC as a Service. This approach targets existing high-end HPC resources and investigates how a Cloud abstraction can be applied to provide a simple interface and support real-world applications. In particular, the application of Clouds to supercomputers is discussed, tested, and validated on an IBM Blue Gene/P supercomputer. The proposed framework transforms Blue Gene/P into an elastic cloud by bridging multiple systems to create HPC federated Clouds, support- ing dynamic provisioning and efficient utilization, and maximizing ease-of-use through an as a Service abstraction. In order to effectively illustrate the benefits of such a concept, the proposed framework is demonstrated using a real-world ensemble application