This chapter discusses mainly impedance matching circuits that are used to match two different terminations. Among the several impedance matching techniques, the available implementation technology is what usually determines the possible matching technique that can be used. Lumped passive matching elements consisting of reactive components (i.e., inductors and capacitors) have become predominant, mainly, with the advent of highly integrated modules and SoCs. Impedance matching using distributed elements also has broad applications in monolithic microwave integrated circuits (MMICs). Matching networks in MICs serve two main purposes. The first is to provide maximum power delivery from a radio frequency (RF) source to a load. The second which has an opposite goal to the first is to limit the amount of power delivered to a system where an impedance mismatch circuit is used to cause power reflection and therefore provides a means of system protection from high power sources. In general, the least complex matching network offers a more reliable and less lossy design. With the different existing matching techniques that a designer can select from, it is feasible to choose a matching network that provides the proper compromise between impedance matching, harmonic attenuation, bandwidth, or network loss.