The use of Josephson mixers with an external local oscillator for sensitive heterodyne reception at submillimeter wavelengths is discussed. Recent experiments, primarily at 450 GHz (0.66 mm wavelength), together with our present theoretical knowledge, allow realistic estimates of future receiver performance to be made. Although some practical problems remain, the probability of building field‐usable receivers with very competitive sensitivity now appears good. A discussion is also given of the use of the high‐harmonic mixing properties of Josephson devices for frequency measurement in the far infrared.