The 5 principles of REST
Contract first approach / Uniform Resource identifiers
Statelessness
Client-Server model
Caching
Layered architecture

Original dissertation

For the last few years, whenever somebody wants to start building an HTTP API, they pretty much exclusively use REST as the go-to architectural style, over alternative approaches such as XML-RPC, SOAP and JSON-RPC. REST is made out by many to be ultimately superior to the other “RPC-based” approaches, which is a bit misleading because they are just different.