RF-MEMS, or MEMS with radio-frequency functionality, were originally developed in the 1990s. Their characteristics in terms of low loss, high isolation and wide tunability were outstanding when compared both to standard RF/microwave components and to semiconductors. Such remarkable performance led many to expect a large adoption of RF-MEMS components in mass-market applications, especially mobile devices and handsets. This revolution was ultimately not realised. However, over the last few years, RF-MEMS have started to make their way into the market landscape, thanks to a need that other technologies were unable to address as effectively. With the advent of modern 4th-generation (4G) smartphones, adaptive impedance tuners are now the first successful example of exploitation of RF-MEMS technology in the consumer market, and ahead of us lies the 5th-generation (5G) of mobile communications and services. 5G will demand an increase in data volume by a factor of 1000, as well as reduced End to End (E2E) latency, Massive Machine Communication (MMC) and operation in the millimetre wave range. RF-MEMS technology promises to be a key enabling solution for 5G. Indeed, 5G could be the killer application scenario for massive uptake of RF-MEMS in the mass-market landscape and offers a vast opportunity for RF-MEMS technology. This book outlines the intrinsic potential of RF-MEMS technology with a specific focus on 5G mobile communications and services. Commencing with a review of the characteristics of RF-MEMS in relation to the specifications of interest for 5G, the book proceeds to develop practical insight concerning the design and development of RF-MEMS including case studies of design concepts. Including multiphysics simulation and animations, the book will be essential reading for both academic and industrial researchers and engineers.