Representational State Transfer is an architectural style for networked APIs, formalized in Roy Fielding's 2000 dissertation. RESTful APIs are characterized by stateless requests, resource- based URL structures, standard HTTP methods (GET, POST, PUT, DELETE, PATCH), and conventional use of HTTP status codes for error signaling.
REST became the dominant API style in the 2010s, displacing earlier approaches like SOAP and XML-RPC. The conventions — pluralized resource URLs, JSON request and response bodies, standard status codes — have become so universal that most developers write "RESTful" APIs without consciously thinking about it.
Pure REST has been partially displaced by GraphQL (for use cases where client query flexibility matters), gRPC (for high-performance service-to-service communication), and now MCP (for AI agent integration). But REST remains the default for public-facing HTTP APIs and is likely to remain so indefinitely. Its combination of conceptual simplicity, ecosystem maturity, and tool support is hard to displace.