The light sources for semiconductor-based optoelectronic devices are LEDs and lasers. LEDs are produced by many Japanese companies. Several companies that have expertise in the AlGaInP materials system - Toshiba and Mitsubishi, for example - have expressed interest in generating highly efficient new red devices for automotive tail lights and highway stoplights. In the United States, Hewlett-Packard is very competitive in these areas. Of course, LEDs are widely used in optoisolators and low-data-rate (<50 Mbit/s) optical links, and in these areas, again, Hewlett-Packard is very competitive. However, this study focuses on emerging device applications: therefore, rather than discuss these LED applications, this chapter will focus mainly on laser developments that seem to indicate emerging new markets. Nevertheless, in the materials section there will be some discussion of LED work in the new II-VI and III-V blue-green materials.