Recent advances in the wireless communication market have led to the coexistence of several networks such as cellular network, personal area network (PAN), wireless local area network (WLAN), etc. along with several different air interfaces (802.11a, 802.11g, Bluetooth, wireless code division multiple access (WCDMA), etc.). Thus, all the wireless devices need to be compatible with the different communication standards while still keeping similar performance, smaller die area and lower power consumption. The need to enable the "global roaming'' capability between a wide variety of networks operating at different frequencies calls for the development of reconfigurable radio-frequency integrated circuits (RFICs) which can achieve maximum hardware sharing between different standards and across various functions. The objective of this dissertation is to present novel topologies for RF components and blocks that can yield a Si-based frequency-agile RF front-end. The targeted applications for this work are 5G multi-band wireless communication and reconfigurable short/long range phased arrays for automobile radars. However, the concept of the proposed reconfigurable RF elements is generic in nature and can be applied to all emerging applications which require on-chip reconfigurability at microwave and mm-wave frequencies.To demonstrate the concept of a reconfigurable RF front end, a Ka/V band-switchable TRX amplifier is developed in 0.13um BiCMOS SiGe process and a 18-50 GHz receiver is developed in 45nm SOI CMOS process. Unlike the traditional approach for a multi-band radio - where the dedicated single band transceivers composed of fixed RF components are designed and multiplexed with the help of switches - the proposed idea utilizes the switches inside each RF block; thus, adding the reconfigurability inside each block and eliminating the need for separate front-ends. However, the catch in the latter approach is to maintain the RF performance while still being able to save the real estate and power consumption. The proposed Ka/V band-switchable TRX amplifier consists of a band-switchable LNA, a band-switchable PA, and integrated T/R switches which saves a lot of area. The band-switch functionality is realized using thin-film microstrip based shunt stubs with reverse saturated SiGe switches. Design techniques for switch loss reduction and size miniaturizations are presented. This work illustrates that with the optimization of switch loss, appropriate selection of each block between wideband or bandswitching topology and co-design of RF blocks, a highly integrated multi-band transceiver can be designed with the minimal degradation to the RF performance compared to state-of-the-art dedicated single band transceivers. To further explore reconfigurable transceivers, a direct quadrature down-conversion mixer first receiver with active channel select filters has been designed. The receiver supports 200MHz instantaneous RF bandwidth and can be reconfigured to receive any 200 MHz channel within 18-50 GHz frequency range. With the ever-evolving wireless standards like 4G/5G/6G, equipment manufacturers are required to add more functionality into the chips while still maintaining the backward compatibility with previous standards or fallback option to lower frequency bands. A low power, highly integrated, multi-band and multi-standard chipset has thus become a requisite in commercial products. The proposed concept of in-block reconfigurability and the presented design techniques to realize mm-wave frequency reconfigurable transceivers have a huge potential in this regard.