Integrated optical instruments and their components are described by comparison with existing technology and the potential advantages of the new systems are outlined. Fundamental problems of material fabrication need to be overcome before a truly integrated circuit becomes feasible but useful advances are being made by combining discrete with integrated components in hybrid systems. A very large investment programme in R & D is underway in Europe, the U.S.A. and Japan. The first products to emerge in instrumental form have not yet had a significant influence on industrial and commercial markets. Future prospects will depend upon improvements in capability, reliability and on cost reductions.