Computer networks allow computers to communicate with one another, and of course form the backbone of the Internet. Although computer networks are becoming a critical infrastructure of our information-based society, they still have not achieved a reliability level of the traditional telephone networks. Research on computer networks at Yale concentrates on designing highly robust and efficient Internet backbone networks, by combining computer science with optimization, economics, and game theory techniques. Besides backbone network management, projects at Yale also address application specific issues. Peer-to-peer (P2P) is emerging as a new paradigm for network application development, as witnessed by the wide usage of P2P file-sharing and video-streaming applications. However, these applications not only generate a large volume of traffic, but also may unnecessarily spread traffic all across the whole Internet, leading to inefficiency. Research projects at Yale are designing effective architecture and algorithms to improve both P2P application performance and Internet operation efficiency.