Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Cloud APIs are Application Programming Interfaces into the Cloud Computing space and specific to how applications and their source code interact with the Cloud. A Cloud API is a mechanism by which software can request information from one or more Cloud Computing Platforms through a direct or indirect interface into a Cloud Computing Platform. Cloud APIs are most commonly written to expose their interfaces as REST and/or SOAP. Being that most Public Clouds are web based, power web applications, and provide interfaces and management utilities that are web based, most use an open REST style architecture for their Cloud APIs.