Wireless communications offer organizations and users many benefits such as portability and flexibility, increased productivity, and lower installation costs. Wireless technologies cover a broad range of differing capabilities oriented toward different uses and needs. This chapter classifies wireless network security threats into one of nine categories: Errors and omissions; fraud and theft committed by authorized or unauthorized users of the system; employee sabotage; loss of physical and infrastructure support; malicious hackers; industrial espionage; malicious code; foreign government espionage; and, threats to personal privacy. All of the preceding represent potential threats to wireless networks. However, the more immediate concerns for wireless communications are fraud and theft, malicious hackers, malicious code, and industrial and foreign espionage. Theft is likely to occur with wireless devices due to their portability. Authorized and unauthorized users of the system may commit fraud and theft; however, the former are more likely to carry out such acts. Since users of a system may know what resources a system has and the system security flaws, it is easier for them to commit fraud and theft. Malicious hackers, sometimes called crackers, are individuals who break into a system without authorization, usually for personal gain or to do harm. Malicious hackers are generally individuals from outside of an organization (although users within an organization can be a threat as well). Such hackers may gain access to the wireless network access point by eavesdropping on wireless device communications. Malicious code involves viruses, worms, Trojan horses, logic bombs, or other unwanted software that is designed to damage files or bring down a system. Industrial and foreign espionage involve gathering proprietary data from corporations or intelligence information from governments through eavesdropping. In wireless networks, the espionage threat stems from the relative ease in which eavesdropping can occur on radio transmissions. This chapter provides an overview of wireless networking security technologies most commonly used in an office environment and by the mobile workforce of today. Also, this chapter seeks to assist organizations in reducing the risks associated with 802.11 wireless LANs, cellular networks, wireless ad hoc networks and for ensuring security when using handheld devices.