The Internet is a recent creation, both theoretically and architectully. Both the theory underlying the Internet and first attemts at implementation date from the 1960s.
The theoretical work responsible of the Internet date to the early 1960s. During this period, the United States Department of Defense (DoD), pondered the question of how to retain communications in the event of nuclear war with the Soviet Union. It was apparent that existing communciations systems would not be survivable in such an eventuality. In 1962-64, a RAND Corporation researcher, Paul Baran, developed a paper entitled "On Distributed Communications Networks", which provided the theoretical background for data communications over an unreliable network.
Baran's paper postulated many of the features of today's Internet -- digital packetized rather than continuously streaming data, individually addressed of data packets, potentially different routes for individual data packets belonging to the same data flow, and an underlying network about which no assumptions concerning reliability are made (a more detailed summary of the network design principles proposed by Baran are listed here)[1]. Baran's concepts were, however not initially regarded as feasible by DoD.
However, a few years later Baran's ideas for packet switched communications were improved upon by Lawrence G. Roberts and proposed to as a design for a packet-switched network at the 1967 ACM Symposium on Operating Principles [2]in Gatlingberg, TN. The proposal was well received by ACM; it was presented to the DoD Advanced Projects Research agency (ARPA) in 1968. The ARPA Network (ARPANET) was commissioned by ARPA the following year as a research project in computer networking.