Representational State Transfer (REST) is an architectural style that defines the architectural quality attributes of the World Wide Web, seen as an open, loosely coupled, massively distributed and decentralized hypermedia system. REST has seen a large uptake for the last several years, as it is largely regarded as a simpler and more Weblike way of exposing service interfaces, in particular when compared with earlier approaches such as the rather complex and heavyweight SOAP/WS-* and similar RPC-inspired protocols. As with all success stories, there also is the downside that pretty much any HTTP-based service is being promoted and sold as being “RESTful” these days, even though many do not completely follow the architectural principles and constraints underlying the REST style [81]. However, in the end this may be the fate of every successful “brand name”: once it becomes successful enough, it loses its purity and is used for marketing, where technical accuracy is not the main concern. The goal of this book is to present the latest developments and advances in research around the topic of REST, and how the Web is changing from a distributed hypermedia system for document publishing to a programmable medium which is more and more being used to deliver software as a service. We have collected many important contributions exending the scope of applicability of REST, proposing to update REST to fit with modern requirements, discussing how to model and describe RESTful architectures, as well as dealing with some of its limitations (eg, observing