This chapter examines the virtualization of services and technologies within the extended network enterprise. Virtualization of applications involves the creation of an application package that is made available to users automatically or on demand. Virtual appliances consist of preconfigured virtual systems with their own operating system, applications, and settings. These systems can provide an excellent mechanism for distributing entire software environments without requiring installation of packages on a host system, beyond the virtualization service itself. Virtualization of multiple physical servers onto more powerful centralized hosts within the data center can provide significant cost savings in terms of hardware, energy, and cooling requirements. Virtualization of networks beyond simple desktops and servers can afford an enterprise with opportunities for modeling, testing, and defense. When the network, servers, and infrastructure are virtualized and resources are made available automatically from a pool of systems, the result is termed cloud computing.