The ARPANET (Advanced Research Projects Agency Network) is widely considered to be the first network that laid the groundwork for the Internet. ARPANET was developed by the United States Department of Defense's Advanced Research Projects Agency (ARPA) and became operational in 1969. It was a pioneering packet-switching network that connected computers at various research institutions and allowed them to communicate with each other. ARPANET played a crucial role in the development of the protocols and technologies that later evolved into the modern Internet.