This article presents methodical techniques to design reconfigurable RF circuits. The methodology begins with component selection to accommodate the circuit design specifications, and a variety of useful components are reviewed including varactors, PIN diodes, substrate- integrated waveguides (SIW), resonators , MEMS switches, π-shaped networks of diodes, phase-change materials and digitally tunable capacitors. A criterion to select components is illustrated along with a summary of performance achieved by various techniques in prior work by others.