The two-volume set LNCS 3420/3421 constitutes the refereed proceedings of the 4th International Conference on Networking, ICN 2005, held in Reunion Island, France in April 2005.The 238 revised full papers presented were carefully reviewed and selected from 651 submissions. The papers are organized in topical sections on grid computing, optical networks, wireless networks, QoS, WPAN, sensor networks, traffic control, communication architectures, audio and video communications, differentiated services, switching, streaming, MIMO, MPLS, ad-hoc networks, TCP, routing, signal processing, mobility, performance, peer-to-peer networks, network security, CDMA, network anomaly detection, multicast, 802.11 networks, and emergency, disaster, and resilency.