"The first chapter gives an overview of cloud computing at a level accessible to a lay person. To motivate the reasons for a paradigm shift in the way we compute and store information, we introduce the concept of network-centric computing and network-centric content. A brief discussion of peer-to-peer systems, a first step in the shift from local to remote data storage and processing follows. The chapter continues with a discussion of technological advances that have made cloud computing possible and of the economical reasons why this new paradigm is attractive for many users and applications. Then we take a closer look at the cloud computing delivery models, Software as a Service (SaaS), Platform as a Service (PaaS), and Infrastructure as a Service (IaaS). SaaS gives the users capability to use applications supplied by the service provider but allows no control of the platform or the infrastructure. PaaS gives the capability to deploy consumer-created or acquired applications using programming languagesand tools supported by the provider. IaaS allows the user to deploy and run arbitrary software, which can include operating systems and applications. The new paradigm raises ethical questions and has significant vulnerabilities each dissected in separatesections. Finally, the chapter presents the major challenges faced by this new paradigm. The chapter concludes with a overview of the literature and with a historic perspective"--