Optical fibre offers a virtually limitless communications bandwidth when used as the physical medium for a local-area network (LAN). However, conventional multiple-access schemes are limited in their ability to exploit this potential. Direct-sequence spread-spectrum systems are a class of code division multiple-access (CDMA) systems that encode data using high-rate sequences to spread data over a much wider bandwidth than normally required for transmission. The paper first considers the problems to be overcome in the design of future high-speed optical networks and then suggests the application of CDMA techniques as a possible solution. There follows an introduction to basic CDMA principles which is then extended to cover the particular coding, modulation and processing considerations to be taken into account when applying CDMA to an optical medium. These considerations are then used to develop a classification scheme which forms the basis for a review of current approaches in the application of CDMA techniques to optical-fibre local-area networks.