50 years ago today, Leonard Kleinrock, submitted his PhD thesis proposal at MIT, “Information Flow in Large Communication Nets,” establishing, in his words, “the underlying principles of data networks that are the basis of the Internet.” From the citation for the most recent award Kleinrock received, the Dan David Prize: “Leonard Kleinrock has made seminal research contributions in communication networks, establishing the fundamental principles upon which many of the most important aspects of computer networking and information communications are based. He developed the key mathematical background to packet switching, the fundamental building block of the Internet. Furthermore, his theoretical work on hierarchical routing is now critical to the operation of today’s world-wide Internet.”