In this article we go through some basic concepts with the purpose of providing context for the discussions in the chapters that follow. Here, we review briefly the concept of the cloud as defined by the U.S. National Institute of Standards and Technology, and the familiar terms of IaaS, PaaS, and SaaS under the SPI model. What is not often discussed is that the rise of cloud computing comes from strong historical motivations and addresses shortcomings of predecessor technologies such as grid computing, the standard enterprise three-tier architecture, or even the mainframe architecture of many decades ago.