This tribute to Professor Leonard Kleinrock highlights his significant contributions to computer communication networks, packet switching, and the development of the Internet. Born in 1934, Kleinrock was a key figure in the early days of packet switching and the ARPAnet, which laid the foundation for the modern Internet. His work in queueing theory and network performance modeling has had a lasting impact on the field. Kleinrock's teaching style and mentorship have influenced many students, including Parviz Kermani, who recalls how his first encounter with Kleinrock changed his life. Kleinrock's research has led to numerous innovations, including the development of the Cut-Through Switching technique, which is used in high-speed switches and routers. His two books on queueing theory remain standard references in network performance modeling. He has also contributed to various areas of computer networking, including hierarchical routing, flow deviation, and virtual cut-through. His work has been widely cited, with many of his papers influencing the development of modern networking technologies. The special issue of Computer Networks includes reprints and updates of some of Kleinrock's most influential papers, such as his work on virtual cut-through and flow deviation. These papers continue to be relevant in the context of modern networking technologies like software-defined networks (SDN). The issue also features contributions from Kleinrock's former students and colleagues, reflecting on his impact on their careers and the field of computer networking. The tribute acknowledges Kleinrock's enduring legacy and the continued relevance of his work in the evolving landscape of computer communication networks.This tribute to Professor Leonard Kleinrock highlights his significant contributions to computer communication networks, packet switching, and the development of the Internet. Born in 1934, Kleinrock was a key figure in the early days of packet switching and the ARPAnet, which laid the foundation for the modern Internet. His work in queueing theory and network performance modeling has had a lasting impact on the field. Kleinrock's teaching style and mentorship have influenced many students, including Parviz Kermani, who recalls how his first encounter with Kleinrock changed his life. Kleinrock's research has led to numerous innovations, including the development of the Cut-Through Switching technique, which is used in high-speed switches and routers. His two books on queueing theory remain standard references in network performance modeling. He has also contributed to various areas of computer networking, including hierarchical routing, flow deviation, and virtual cut-through. His work has been widely cited, with many of his papers influencing the development of modern networking technologies. The special issue of Computer Networks includes reprints and updates of some of Kleinrock's most influential papers, such as his work on virtual cut-through and flow deviation. These papers continue to be relevant in the context of modern networking technologies like software-defined networks (SDN). The issue also features contributions from Kleinrock's former students and colleagues, reflecting on his impact on their careers and the field of computer networking. The tribute acknowledges Kleinrock's enduring legacy and the continued relevance of his work in the evolving landscape of computer communication networks.