The forms that cities take, the ways they function, and the mixes and distributions of activities within them have always been influenced very strongly by the capabilities of their underlying network infrastructures. Furthermore, cities have often been transformed by the introduction of new infrastructures. It is impossible to imagine Rotterdam without its canals and connection to the North Sea, Chicago without its railroads, Los Angeles without its freeways, or any large modern city without water supply, sewage, electrical, and telephone networks. Today, a new type of network infrastructure — high speed digital telecommunications — is being overlaid on cities everywhere. Its effects will be at least as revolutionary as those of the new network infrastructures of the past. It is already causing traditional building types and neighborhood patterns to fragment, recombine, and form startling new arrangements. This process will continue and accelerate. In this paper I describe the new digital infrastructure, analyze its major spatial effects, consider some illustrative examples of the resulting fragmentation and recombination, and discuss possible design responses with particular attention to social equity and long-term sustainability.