ARPANET was a wide-area network that was developed and established in 1969 by the United States Defense Advanced Research Project Agency. The network served as a platform to test networking technologies and linked together various research centers and universities.

ARPANET is commonly referred to as the precursor of the Internet and was designed to allow information to be exchanged between geographically separated computers. The exchange occurred through a computer communication protocol called the "Network Control Protocol." ARPANET was also used between military installations, allowing for data to reside in multiple computers securely.

The first ARPANET network was made up of four connected computers at UCLA, Stanford Research Institute, UC Santa Barbara and the University of Utah. The first exchange of data over ARPANET occurred between Stanford and UCLA, and the first access attempt was made by UCLA researchers who crashed their computer partially through the initial login attempt. Compatibility problems occurred when more computers joined the network, leading to the development of the TCP/IP protocols in 1982.

Several of the technologies that were developed under ARPANET included electronic mail, telnet and the file transfer protocol. In 1983, military organizations created a separate military-only network called MILNET as ARPANET's security weakened due to the increasing number of users that was able to access it.