This chapter presents some opportunities offered by silicon (Si) nanostructures for photonics and photovoltaics. Several approaches, mainly based on nanoscale engineering, have been developed to extend Si capabilities. The optical properties of c-Si are relatively poor, owing to its indirect band gap that precludes the efficient emission and absorption of light. High optical performances are required to enable true optoelectronic integration and pave the way to faster, highly integrated, and low-cost devices. For photovoltaics applications, higher optoelectronic performance would enable a new generation of high-efficiency Si solar cells. Si nanostructures may offer a range of new opportunities for all of these applications. Applied to photovoltaics, multiple carrier generation (MEG) would create more than one electron-hole pair per single absorbed high-energy photon, thereby creating additional photocurrent from the …