Following the invention of the laser, the understanding of optical phenomena has progressed rapidly and new technologies have emerged with enormous potential for useful application. Among these, the technology of communication by light through glass fibres stands out. This review takes the reader from the concepts and science of light guidance to the challenges of fabricating modern glass fibres and engineering optical systems. It includes a review of the most recent understanding of the physics and chemistry of optical fibres. It illustrates the choices that exist, ranging from a variety of fibre structures to options in operating wavelength and modulation format. The reader finds a discussion of the opportunities that fibre systems present for a variety of communications applications from simple telephone connections to high-capacity ocean cable systems.