The evolution of Si-based optoelectronics has been extremely fast in the last few years and it is predicted that this growth will still continue in the near future. The aim of the volume is to present different Si-based luminescing materials as porous silicon, rare-earth doped silicon, Si nanocrystals, silicides, Si-based multilayers and silicon-germanium alloy or superlattice structures. Moreover, the different devices needed for an all-Si-based optoelectronics are treated, spanning from light sources to waveguides, from amplifiers and modulators to detectors. Both the very basic treatments as well as applications to real prototype devices and integration in an optical integrated circuit are presented. Many still unresolved problems are underlined: the problem of electrical transport in low-dimensional Si systems, the possibility of gain in Si-based systems, the low modulation speed od Si-based LEDs, etc. The book gives a fascinating picture of the state-of-the-art in Si microphotonics and a perspective on what one can expect in the near future. For these reasons, it might be useful not only to graduate students but also to all researchers involved in this field.