It begins with an introduction to the basic ideas behind fixed and random access systems to show the difference between CDMA and TDMA is more widely understood, FDMA or CSMA. Second, the review presented basic spread spectrum technique used in CDMA systems including direct sequence, frequency-hopping and time-hopping approach. The basic concept of CDMA is presented, followed by four basic principles of CDMA systems that impact their performance: the average multiplexing interference, universal frequency reuse, soft handoff, and statistics. A detailed discussion on CDMA-based mobile sound system, especially the IS-95, are presented. Also discussed are Third Generation CDMA cellular systems and how they differ from Second Generation systems.