This article is a tribute to Professor Leonard Kleinrock, celebrating his 80th birthday and recognizing his significant contributions to the fields of queueing theory, packet switching, and computer communication networks. The tribute includes reflections from his former students, friends, and colleagues, highlighting his impact on their professional lives and the development of communication networks. Key contributions mentioned include his foundational work on stochastic models for packet-switched networks, his two influential books on queueing theory, and his pioneering research in areas such as Carrier Sense Multiple Access (CSMA) techniques, virtual cut-through, and hierarchical routing. The article also discusses the ongoing relevance of his work, particularly in the context of Software Defined Networks (SDN) and the resurgence of interest in virtual cut-through. The tribute concludes with a brief overview of the papers included in this special issue, which cover a range of topics from network optimization to energy consumption in WLANs and the application of queueing models to hospital patient flow.This article is a tribute to Professor Leonard Kleinrock, celebrating his 80th birthday and recognizing his significant contributions to the fields of queueing theory, packet switching, and computer communication networks. The tribute includes reflections from his former students, friends, and colleagues, highlighting his impact on their professional lives and the development of communication networks. Key contributions mentioned include his foundational work on stochastic models for packet-switched networks, his two influential books on queueing theory, and his pioneering research in areas such as Carrier Sense Multiple Access (CSMA) techniques, virtual cut-through, and hierarchical routing. The article also discusses the ongoing relevance of his work, particularly in the context of Software Defined Networks (SDN) and the resurgence of interest in virtual cut-through. The tribute concludes with a brief overview of the papers included in this special issue, which cover a range of topics from network optimization to energy consumption in WLANs and the application of queueing models to hospital patient flow.