HTTP, the HyperText Transfer Protocol, is the application-level protocol that web clients and servers use to exchange documents. A client opens a connection, sends a request, and the server returns a response; this simple request/response cycle underlies essentially all browsing on the Web.
The first version, retroactively called HTTP/0.9, was the protocol as originally implemented by the World Wide Web software. The CERN documentation describes it as a deliberate subset of the full protocol: a client connects over TCP/IP to port 80, sends the single word “GET” followed by a document address on one ASCII line, and the server replies with an HTML byte stream and then closes the connection. There were no headers, no status codes, and no metadata; the server “need not store any information about the request after disconnection.”
As the Web grew, the protocol was formalized through IETF RFCs. RFC 1945, “Hypertext Transfer Protocol — HTTP/1.0,” was published in May 1996 by Tim Berners-Lee, Roy Fielding, and Henrik Frystyk; it documents common usage of the protocol and notes that “HTTP has been in use by the World-Wide Web global information initiative since 1990.” HTTP/1.0 added request and response headers, status codes, and content typing. HTTP/1.1 followed and introduced persistent connections and other refinements that made the protocol practical at internet scale.
HTTP’s strength was its simplicity. A protocol that started as a single line of text grew, without breaking, into the foundation for the modern Web, later layered over TLS as HTTPS for security.