This chapter introduces the concept of cloud computing. It describes its definition, presents the cloud delivery and deployment models, and highlights its benefits for enterprises. The last part of the chapter identifies the primary pre-requisites for cloud computing, namely, virtualization and service-oriented computing. The virtualization system is a key foundation for the cloud computing system. We stitch together compute resources so as to appear as one large computer behind which the complexity is hidden. By coordinating, managing, and scheduling resources such as CPUs, network, storage, and firewalls in a consistent way across internal and external premises, we create a flexible cloud infrastructure platform. This platform includes security, automation and management, interoperability and openness, self-service, pooling, and dynamic resource allocation. Cloud computing builds on virtualization to create a service-oriented computing model. This is done through the addition of resource abstractions and controls to create dynamic pools of resources that can be consumed through the network. Benefits include economies of scale, elastic resources, self-service provisioning, and cost transparency. Consumption of cloud resources is enforced through resource metering and pricing models that shape user behavior. Consumers benefit through leveraging allocation models such as pay-as-you-go to gain greater cost efficiency, lower barrier to entry, and immediate access to infrastructure resources.