Publisher Summary This chapter discusses the successes and challenges encountered in the realization of silicon photonic integrated circuits (PICs). Silicon photonics refer to the implementation of integrated optics and PIC technologies in silicon. Beyond the advantageous use of silicon substrates, silicon is used as an optical or wave-guide medium, and an active medium for modulation, tuning, or switching. Huge amounts of investment, innovative design, process discipline, and large-volume runs made have led to economic success. The prospects of fabricating PICs using silicon to capitalize on the investment have led to the success of silicon ICs. To succeed one requires a large-volume application and a design that can be made in an operating silicon IC foundry facility. A potential advantage is the opportunity to incorporate electronic signal processing on the same photonic chip. While silicon has proven to be the ideal material for electronic ICs, it is far from ideal for PICs. Its shortcoming is the inability to make a good light source or photo detector in silicon.