The mathematical theory of packet networks is the technology underpinning the internet, everything carried out via the internet involves packets. For example, simple tasks such as uploading an image and sending an e-mail. Networks that ship data in small packets are called packet switched networks.

Kleinrock's first paper on digital network communications and information flow in large communication nets was published in July 1961, present in the RLE Quarterly Progress Report. Leading to the expansion on his ideas in his 1963 Ph.D. theory, proved by publishing a comprehensive analytical treatment of digital networks in his book "Communication Nets" during 1964. Once his theory was completed, Kleinrock moved to UCLA and established the Network Measurement Center (NMC), using his knowledge and skills to lead a group of graduate students working in the area of digital networks. During the year of 1966, Kleinrock's theory was used by Lawrence Roberts to convince colleagues of the possibility of a wide area digital communication network. A contract was given to Kleinrock's National Measurement Centre in October 1968 to carry out ARPANET performance measurement and find areas for improvement. Early September 1969, a team at Kleinrock's NMC connected one of their SDS Sigma 7 computers to an Interface Message Processor thus, successfully enabling the first node on the ARPANET, and the first computer ever on the Internet.

The group continued their research into the ARPANET as it grew in the early 1970's, working to solve performance issues. Kleinrock himself, also progressed in his research. He has published his life work and knowledge into 200+ papers and 6 books.

When questioned on the future of technology, Kleinrock states;

"I see small, pervasive devices ubiquitously embedded in the physical world, providing the capabilities of actuators, sensors, logic, memory, processing, displays, cameras and so on. I see all these things and more as we move headlong into the 21st century of everywhere access to what I like to call 'smart spaces.' Indeed, I foresee that the Internet will essentially be an invisible infrastructure serving as a global nervous system."