This chapter deals with the development of optical functionality on a silicon platform holds great promise for the widespread deployment of integrated circuits that combine photonics and microelectronics and reviews the physics that underpins optical waveguiding in silicon. It discusses the choice of silicon as a substrate for the fabrication of optical waveguides which follows naturally from its domination of microelectronics. The chapter briefly reviews the histories of silicon electronic devices and integrated circuits. It explains the vast majority of work on silicon waveguides that has focused on the use of silicon-on-insulator. The chapter describes several essential elements required of a highly integrated optoelectronic system and how they may be fabricated using a silicon substrate. It witnesses the increased migration of silicon photonics from the research laboratory to the manufacturing facility with benefits to the areas of microelectronics, telecommunications, biological, environmental, and medical sensor industries.