Multi-standard and multi-band radio are the next milestone in the ever developing radio industry. Frequency agile circuits are an enabling technology which allows us to achieve this goal. It is a low cost and efficient technology that provides the nec-essary flexibility required to implement multi-standard and multi-band radios. One important circuit component which comes easily to one’s mind for frequency tunabil-ity is a varactor; with so many constraints of high tuning range, fast tuning speed and low loss on varactor, new technologies have come up to full fill these require-ments. Among various varactor technologies, Barium Strontium Titanate (BST) has shown promise in the implementation of various tunable circuits like filters, voltage controlled oscillators (VCO), and tunable matching networks with good performance. This thesis concentrates on the use of BST for implementation of frequency agile circuits. Two circuits which form an integral part of any RF transreciever are a VCO and a low noise amplifier(LNA). These circuits were chosen to demonstrate the usability of BST varactor as a tunable element. The VCO implementation shows how a BST varactor can be integrated with modern integrated circuit process like