Spread spectrum signals typically refer to signals that use a bandwidth that is significantly higher than the minimum bandwidth required transmitting that information sequence. The early developments in spread spectrum systems were primarily in military applications, where the low probability of intercept and antijam features were especially useful. For instance, commercial applications of spread spectrum in the cellular wide area networks are similar to the military predecessors in many aspects. The chapter discusses direct sequence spread spectrum systems. It focuses on frequency hopping systems. In a frequency hopping spread spectrum system, the actual signal transmitted has narrow bandwidth. The chapter highlights some of the important applications of spread spectrum signals. The Bluetooth technology is an excellent example that demonstrates the commercial success of spread spectrum technology in enabling multiple independent peer-to-peer networks to simultaneously operate in the same geographical area.