In this chapter we examine, in a systematic manner, some of the issues about Fielding's doctoral dissertation that have caused so much confusion. We start examining REST as an architecture style as a sequence of architectural decisions. We use then influence diagrams to build a model that allows us to see how the architectural decisions take us from classic architectural styles like client-server and layered-system to REST. The graphical model not only facilitates the understanding of this important new architectural style, but also serves as a framework to assess the impact of relaxing or adding more constraints to it. As a final example we analyze the resource-oriented architecture (ROA) to find out one important constraint that is present in REST is missing in ROA and this has an impact on both scalability and modifiability.