This thesis is concerned with the development of a general and rigorous broadbanding theory for varactor parametric amplifiers. Fundamental gain bandwidth limitations of a varactor parametric amplifier are obtained which are independent of the equalizer. Results obtained in this theory lead to the design and synthesis of broadband varactor parametric amplifiers. The circuit considered in this thesis is that of linear variable capacitors embedded in an arbitrary, passive, lossless environment in which the signal frequency and one of the sideband frequencies can exist. In the course of developing a broadband ing theory, some fundamental inherent properties of a parametric device are revealed. The first is that the varactor, when embedded in an arbitrary, passive environment, presents an impedance which can be characterized by a positive function rather than a positive-real function. The second and more important inherent property is that, due to the frequency-coupling action of the variable capacitor, the scattering coefficient at the varactor port is quadratic in nature. A broadbanding theory has been obtained, taking into account both of these properties. Some realizability conditions are presented which are indicative of the inherent properties of a parametric device.