Cloud computing evolved from cluster computing, allowing enterprise customers to migrate their business information systems to the cloud without modification. Compared to cluster computing, cloud computing once again elevates resource sharing to a whole new level. On the basis of cluster computing, cloud computing further addresses two key issues: (1) enterprise customers’ applications can run successfully everywhere on the cloud; (2) multiple applications running on the same computer do not interfere with each other. This chapter structured an application into two parts: the application itself and the runtime environment, and then explain how to solve these two problems by virtualization. The involved knowledge includes execution based on compilation, execution based on interpretation, the implementation of interpreter, virtualization of the runtime environment, virtual function, the effect of virtual file, network virtualization, overlay network, migration of applications, virtual machines (VMs), persistent storage of VMs, container, containerization of applications, Namespace, CGroup, Docker, and Kubernetes. This chapter will uncover the mysterious veil of virtualization technologies by cases, presenting a concise implementation of VM.