Growth in the number of transistors per die of an integrated circuit has provided impetus to the development of system-on-chip microprocessors (SoCs). They are becoming ubiquitous and appear in home appliances, cell phones, tablet, laptop, and desk-top computers, and lately even as building blocks in high-end computer systems. As the semiconductor manufacturing technology progresses in concert with Moore’s law, SoCs clearly represent the trend of the future of microprocessor design. SoCs vary widely in composition, complexity and sophistication depending on the computing applications for which they are intended: some are simple single-processor systems, while others range from a few to a few tens of processor cores and contain other hardware functional blocks, storage elements, memory controllers and interfaces to external high-speed interconnections such as PCI Express, SRIO, and others. In any such SoC, the on-chip interconnections play a central role in its operation and contribute vitally to the performance of the applications running in it. This chapter explores the choices of interconnections that may be employed and discusses the criteria for their selection. The chapter illustrates the interconnection selection process by describing an example SoC and examining the interconnections it contains.