The Advanced Research Projects Agency Network (ARPANET) was an early packet switching network and the first network to implement the protocol suite TCP/IP. Both technologies became the technical foundation of the Internet. The ARPANET was initially funded by the Advanced Research Projects Agency (ARPA) of the United States Department of Defense.

The packet switching methodology employed in the ARPANET was based on concepts and designs by Americans Leonard Kleinrock and Paul Baran, British scientist Donald Davies, and Lawrence Roberts. The TCP/IP communications protocols were developed for the ARPANET by computer scientists Robert Kahn and Vint Cerf, and incorporated concepts from the French CYCLADES project directed by Louis Pouzin.

As the project progressed, protocols for internetworking were developed by which multiple separate networks could be joined into a network of networks. Access to the ARPANET was expanded in 1981 when the National Science Foundation (NSF) funded the Computer Science Network (CSNET). In 1982, the Internet protocol suite (TCP/IP) was introduced as the standard networking protocol on the ARPANET. In the early 1980s the NSF funded the establishment for national supercomputing centers at several universities, and provided interconnectivity in 1986 with the NSFNET project, which also created network access to the supercomputer sites in the United States from research and education organizations. The ARPANET was decommissioned in 1990.

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