This document discusses spread spectrum techniques. It begins with a brief history, noting that spread spectrum was invented in the 1940s as a way to prevent enemy detection of radio signals, and gained popularity due to its resistance to jamming. The document then provides an overview of spread spectrum systems, classifications (direct sequence, frequency hopping, time hopping), applications (resistance to interference and jamming, security, CDMA), and comparisons of techniques and their advantages/disadvantages.