Swept-measurement techniques are developing rapidly and have demonstrated their crucial importance in advancing the microwave state-of-the-art. The key components of swept-measurement systems are discussed and the development of reflection coefficient measurements on a swept basis is examined in detail. Reflectometer and slotted-line accuracies are analyzed using signal flow graphs. The results are compared to illustrate that in the typical laboratory, swept-frequency measurements offer accuracy equivalent to the slower, more tedious, fixed-frequency systems. A significant step forward has been the development of instrumentation to completely characterize high-frequency networks by means of the complex scattering matrix. The new techniques for sweep-measuring the amplitude and phase of microwave parameters are explained and the s-parameter design procedures which have evolved are referenced.