Silicon (Si) photonics is the science and technology of using the group-IV element of the periodic table as the principle material for optoelectronic integrated circuits (OEICs). Silicon has long had photonic applications. Notably, it has been the dominant material of choice for photovoltaic cells, visible and short near-infrared (IR) (<1?µm wavelength) photodetectors, as well as for X-ray detectors in conjunction with scintillators. However, the younger field of silicon photonics is less related to these traditional applications. Rather, it refers to performing a wide range of passive and active optical functionalities on an integrated circuit at wavelengths within the material’s transparency range, i.e., above the bandgap cutoff of 1.1?µm. Particularly, the telecommunication wavelengths of 1.3-1.6 µm and more recently the longer wavelengths of the mid-IR-up to ~6.7?µm beyond which the material becomes lossy-are the realm of silicon photonics. Based on some interesting waveguide platforms, silicon is recognized as an ideal material for low loss and ultracompact passive integrated optics at these wavelength ranges. There are also means to achieve optical modulators on the material. Heterogeneous integration of Si with devices on germanium (Ge), silicon-germanium (Si-Ge) alloys, and III-V compound semiconductor materials has allowed achieving detection and generation and amplification of optical waves in the near IR range.