The enormous progress of communication technologies in the last years has increased the demand for efficient and low-cost optoelectronic functions. For several present and future applications, photonic materials—in which light can be generated, guided, modulated, amplified, and detected—need to be integrated with standard electronic circuits in order to combine the information-processing capabilities of electronics data transfer and the speed of light. Long-distance communications, local-area-networks data transfer, and chip-to-chip or even intrachip optical communications all require the development of efficient optical functions and their integration with state-of-the-art electronic functions. Silicon is the material of choice for reliable and low-cost optoelectronic integrated circuits because it is the leading semiconductor in the electronic arena and since a wellestablished processing technology exists for this material. However Si is characterized by an indirect bandgap and by a weak electro-optic effect. It is therefore not suitable for the implementation of fundamental optical functions such as light emission and modulation. At the moment, hybrid integration of compound-semiconductor optical functions with Si electronic functions is providing the gateway from electronic to photonic technology. However several strategies are being considered to engineer the optical functions of Si and to realize fully Si-based or at least Si-compatible optoelectronics.