This chapter presented diverse methods for tuning microwave filters with the objective of providing an overall view of the field. The filters discussed in this chapter were classified by the technology used to tune filter parameters. Some devices are miniature type lumped element filters and others involve distributed designs with larger size but higher resonator unloaded quality factors in general. The chapter covered filters made using different technologies including active devices, MEMS, ferroelectric and ferromagnetic materials. Filters involving combined technologies were covered; and also the traditional tuning using mechanically adjustable screws was discussed. In this section a general technology summary is provided, pointing out some important features and drawbacks associated with each technology. Microwave tunable filters can reconfigure filter parameters like center frequency, bandwidth or selectivity in a discrete or continuous fashion, according to the tuning element used to reconfigure the given filter parameter. One important issue to look at is the operating frequency range of the filters according to the technology used for its fabrication. Diode tuned filters have been used at design frequencies ranging from VHF to X band (0.03 ­ 12.4 GHz). Filters made using MEMS technology have high potential of operating at much higher frequencies compared to diodes, for instance filter designs can be found with an operating frequency range from VHF to U band (0.03 ­ 60 GHz). Capacitive MEMS tuning elements have been used for high frequency operation, and direct contact type MEMS actuators are normally used for low frequency operation. Ferroelectric tuned filters have been mainly focused on operating frequency ranges from VHF to K band (0.03 ­ 26.5 GHz) where some few designs have center frequencies up to U band (60 GHz). Ferromagnetic tuned filters have been used in general for operating frequencies up to K-band. Diodes have the advantage of being most of times a low cost tuning technology, where also fully monolithic designs can present the possibility of high integration with other