This chapter provides a brief overview of wireless systems and standards. The evolution of wireless systems from voice-centric circuit-switched systems to data-centric packet-switched systems is discussed. The first- and second-generation wireless systems were designed primarily for voice service. The data rate supported by these systems is very limited. The 2.5G systems were developed to retrofit second-generation systems to support higher data rate applications. The third-generation systems are designed to meet the demands of the Internet era. A wide range of IP-based services is provided using these systems. IEEE 802.16 standard-based systems, commonly referred to as WiMAX, are being proposed as an alternative to third-generation systems for carrying data traffic. Popular wireless LAN and wireless PAN standards are also discussed.