This book describes in detail the impact of process variations on Network-on- Chip (NoC) performance. The authors evaluate various NoC topologies under high process variation and explain the design of efficient NoCs, with advanced technologies. The discussion includes variation in logic and interconnect, in order to evaluate the delay and throughput variation with different NoC topologies. The authors describe an asynchronous router, as a robust design to mitigate the impact of process variation in NoCs and the performance of different routing algorithms is determined with/without process variation for various traffic patterns. Additionally, a novel Process variation Delay and Congestion aware Routing algorithm (PDCR) is described for