Abstract: Switches are key components with convert microwave signals. Compared to conventional (usually semiconductor) switches, RF MEMS switches have superior high frequency performance. Furthermore, the fabrication technology of RF MEMS switches is compatible with that of CMOS. In this paper, the operation principle and typical performance parameters of series cantilever beam switches, shunt cantilever beam switches and membrane switches are discussed in detail. Because of their superior microwave performance, MEMS switches are being developed in many circuits and systems, including radio front ends, capacitor banks and phase shifting networks.