As we enter the many-core era, the interconnection networks of a computer system, rather than the processor or memory modules, will dominate its performance. Several recent developments in interconnection network architecture including global adaptive routing, high-radix routers, and technology-matched topologies offer large improvements in the performance and efficiency of this critical component. The implementation of a portion of several interconnection networks on multi-core chips also raises new opportunities and challenges for network design. This talk explores the role of interconnection networks in modern computer systems, recent developments in network architecture and design, and the challenges of on-chip interconnection networks. Examples will be drawn from several systems including the Cray BlackWidow.