Cloud computing is a flexible and affordable way to address and fulfill the need of high-range computing facilities for end-users. Flexibility with cloud systems, beside the typical pay-as-you-go characteristic, applies to hardware configuration and tasks scheduling associated to specific applications. High-performance computing (HPC), which aims at offering a fast computing solution from the machines and the programming standpoints, has also adopted the cloud computing paradigm and associated systems as a serious alternative. However, the strong requirement of efficiency w.r.t HPC implementations raises several questions and concerns when it comes to the deployment on the cloud. To understand the main points and guide the thoughts for scientific and technical investigations, it is important to understand the key aspects of HPC. This is the aim of the current chapter, which provides a view of the HPC landscape and techniques, so as to help for a better understanding of this specific context.