Book excerpt: Software-Defined Radio (SDR) represents the next revolution in Radio Receiver technology embodying an efficient technique for radio transceiver design boasting of multiple advantages in terms of adaptability and re-configurability to support new waveforms and multi-functionality in terms of supported bands, modes of operation, and air interfaces. This thesis presents a review of flexible RF front-ends for use in SDR supporting multiple waveforms. The requirements for an illustrative SDR RF front-end supporting some of the popular wireless standards is examined and the possibility of multi-standard operation is discussed in terms of receiver performance and the architectures that enable its realization.