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This paper describes coherent sources of radiation useful in the near-millimeter-wavelength spectrum, generally taken to span the range of about 80 to 1000 GHz; however, both optically pumped and discharge pumped lasers are excluded from this treatment, since these devices are adequately covered elsewhere. Included in this discussion are solid-state sources such as IMPATTs and Gunn devices; tube sources such as klystrons, magnetrons, and backward-wave oscillators; and newer sources including TUNNETTs, gyrotrons, and relativistic electron-beam devices. Because of the large amount of material to be covered, the treatment is limited to a brief description of each device and an enumeration of its capabilities; no attempt is made to give a detailed discussion of device physics, as references are available for this purpose. Phase and frequency control of near-millimeter-wave sources is becoming increasingly important because of applications of this spectrum to Doppler radar, communication, and measurement systems. The paper concludes with a presentation of phase and frequency control results for both tube and solid-state sources.