Using the HTTP protocol, REST APIs allow software on one device to talk to software on another device (or the same device) even if they use different operating systems and architectures. Often referred to as RESTful web services, REST uses HTTP methods to retrieve and post data between a client device and a server. Most commonly, developers use REST APIs to build web services. REST API (Representational State Transfer Application Program Interface) is an architectural style that allows software to communicate with other software over a network or on the same device.