Wireless networks and communications are becoming an integrated part of people’s everyday work and life. Mainly due to the nature of unconfined signal transmitted in air and relatively limited computation power and battery resources, designing and implementing security mechanisms in wireless networks is much more challenging than in wired environments. This chapter provides an overview of the applications, technologies, and standards of secure wireless networks and communications. As each type of wireless networks has its own characteristics and supports different applications, the technical details of security goals, technologies, and standards are elaborated in each of the following chapters.