The original ARPANET, one of the components which evolved eventually into the Internet, connected four Universities: University of California Los Angeles, University of California Santa Barbara, Stanford Research Institute and Utah University. The IMPs, interface minicomputers, were built during 1969 by Bolt, Beranek and Newman in accord with a proposal by the US Department of Defense Advanced Research Projects Agency, which funded the system as an experiment. By 1973 it connected many more systems and included satellite links to Hawaii and Scandinavia, and a further link from Norway to London. ARPANET continued to grow in size, becoming more a utility than a research project. For this reason during 1975 it was transferred to the US Defense Communications Agency.

During the development of ARPANET, a numbered series of Request for Comments (RFCs) memos documented technical decisions and methods of working as they evolved. The standards of today's Internet are still documented by RFCs, produced through the very process which evolved on ARPANET.

Outside of the USA the dominant technology was X.25. The International Packet Switched Service, created during 1978, used X.25 and extended to Europe, Australia, Hong Kong, Canada, and the USA. It allowed individual users and companies to connect to a variety of mainframe systems, including Compuserve. Between 1979 and 1984, a system known as Unix to Unix Copy Program grew to connect 940 hosts, using methods like X.25 links, ARPANET connections, and leased lines. Usenet News, a distributed discussion system, was a major use of UUCP.

The Internet protocol suite, developed between 1973 and 1977 with funding from ARPA, was intended to hide the differences between different underlying networks and allow many different applications to be used over the same network.

RFC 801 describes how the US Department of Defense organized the replacement of ARPANET's Network Control Program by the new Internet Protocol during January 1983. During the same year, the military systems were removed to a distinct MILNET, and the Domain Name System was invented to manage the names and addresses of computers on the "ARPA Internet". The familiar top-level domains .gov, .mil, .edu,.org, .net, .com, and .int, and the two-letter country code top-level domains were deployed during 1984.

Between 1984 and 1986 the US National Science Foundation created the NSFNET backbone, using TCP/IP, to connect their supercomputing facilities. The combined network became generally known as the Internet.

By the end of 1989 Australia, Germany, Israel, Italy, Japan, Mexico, the Netherlands, New Zealand, and the United Kingdom had connected to the Internet, which now contained over 160,000 hosts.

During 1990, ARPANET formally terminated, and during 1991 the NSF ended its restrictions on commercial use of its part of the Internet. Commercial network providers began to interconnect, extending the Internet.

Today almost all Internet infrastructure is provided and owned by the private sector. Traffic is exchanged between these networks, at major interconnect points, in accordance with established Internet standards and commercial agreements.