An outline of the development of microwave parametric amplifiers (paramps) is presented as an introduction. The principle of their operation is explained leading to the classification of parametric amplifiers and frequency converters. (Photoparametric amplification is also referenced.) Varactor diodes are briefly presented in order to discuss in greater detail the operation of the most significant type of paramp—the nondegenerate parametric amplifier—including gain, noise, bandwidth, and stability. Degenerate, multiple‐idler and traveling‐wave parametric amplifiers are also discussed. Then the construction of a 3.25‐GHz nondegenerate parametric amplifier is presented as a representative example.