Will RF MEMS deliver on its promise to be one of the major MEMS businesses in the future? RF MEMS has now entered its second generation; high-volume production of both contacting and non-contacting switches and filters (based on bulk acoustic waves) was ramped up worldwide starting in 2003. In first-generation RF MEMS, discrete components were developed to demonstrate RF performance and reliability, and low-cost, high-volume chipand wafer-scale packaging eliminated the final barriers to high-volume production of discrete replacement components with MEMS. In this paper, we review the RF MEMS industry and the commercialization status of RF MEMS components. We also provide a detailed case study of mobile telephone basestations, demonstrating how RF MEMS can impact telecommunications. Finally, we look at research into third-generation RF MEMS and NEMS, in which integration, active devices, and new functionality will create opportunities for disruptive changes in RF subsystems, enabling such things as software-defined radio. © 2005 Lucent Technologies Inc.