This book provides a unified overview of network-on-chip router micro-architecture, the corresponding design opportunities and challenges, and existing solutions to overcome these challenges. The discussion focuses on the heart of a NoC, the NoC router, and how it interacts with the rest of the system. Coverage includes both basic and advanced design techniques that cover the entire router design space including router organization, flow control, pipelined operation, buffering architectures, as well as allocators' structure and algorithms. Router micro-architectural options are presented in a step-by-step manner beginning from the basic design principles. Even highly sophisticated design alternatives are categorized and broken down to simpler pieces that can be understood easily and analyzed. This book is an invaluable reference for system, architecture, circuit, and EDA researchers and developers, who are interested in understanding the overall picture of NoC routers' architecture, the associated design challenges, and the available solutions.