Optical-fiber transmission lines appear attractive for a variety of communication applications in which twisted copper pairs and coaxial cables are now used. These applications range from on-premises data links and equipment wiring to interoffice and intercity telecommunication trunks. Experiments to explore the technical feasibility of glass fibers in these areas are presently in progress. The author summarizes the current state of research on optical fibers, fiberguide cables, and splicing techniques, reviews the state of the art of fiber-compatible sources and detectors and discusses various systems considerations, experiments, and applications.