New semiconductor materials and device structures are essential to the development of new types of electro-optical devices and systems in areas such as integrated optics, optical communications, and optical computing. This paper presents a discussion of basic materials requirements, in terms of both optical properties and materials fabrication technologies, for representative electro-optical devices. In the area of optical communications, interest is shifting towards longer wavelengths, which generates the need for sources and detectors operating in the same region. The current status and future possibilities for such devices, as examplified by fast photodetectors, are discussed in terms of new semiconductor alloy materials and device structures. In the areas of optical computing and integrated optics, the basic essential structure is a low-loss optical thin-film waveguide. The materials aspects of such devices are discussed, and the relevant considerations are illustrated through a description of recent work with GeO2 waveguides.