A radio frequency micromachined based phase shifter is one of the key components in a modern electronically steerable phased array for satellite communication, radar systems and high precision instrumentation. The phase shifter controls the signal phase to steer the direction of the beam. MEMS technology provides a superior performance in terms of low loss, low power consumption and excellent linearity compared to other technologies. MEMS based digital phase shifters provide a large phase shift and low sensitivity to electrical noise with a high tuning ratio compared to analog versions. This Chapter describes different types of TTDTrue-time-delayPhotoresist phase shifters utilizing MEMS switches and MEMS varactors. A gold-based surface micromachining process is used to develop different kinds of MEMS phase shifters on alumina (εr = 9.8) substrates. All phase shifters are implemented using coplanar waveguide (CPW) transmission lines and actuated by electrostatic actuations. These include the analog type Distributed MEMS Transmission LineDistributed MEMS transmission line (DMTL) phase shifter using push–pull actuation, a 5-bit DMTL phase shifter using MEMS bridge and a fixed capacitor, 5-bit switched line phase shifter using DC-contact MEMS switches and a 2-bit & 5-bit phase shifter using MEMS SP4T and SPDT switches. This Chapter includes details on the design, development, and characterization of MEMS phase shifters. Furthermore, all experimental results are validated with a circuit analysis and full-wave EM simulation. © 2022, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.