Code division multiple access (CDMA) has proven to be a viable enabling technique for the simultaneous transmission and reception of data over a shared channel. Although associated mostly with wireless cellular communication, CDMA is also being considered for optical channels. This text, aimed at the reader with a basic background in electrical or optical engineering, covers CDMA fundamentals: from the basics of the communication process and digital data transmission, to the concepts of code division multiplexing, direct sequence spreading, diversity techniques, the near-far effect, and the IS-95 CDMA standard form.