This review deals with recent determinations of the intensity of the microwave background radiation at wavelengths too short for direct observation from the ground, the short-wavelength background being defined here as that covering the spectral range from roughly 3 to 0.3 mm. The most important information in this region has been obtained directly from far-infrared telescopes carried above the lower atmosphere by rockets and balloons, and indirectly from ground based optical and radio observations of interstellar molecules. The essential ques tion to be considered-of very great interest to both cosmology and high-energy astrophysics-is whether the short-wavelength spectrum is that of a '3°K black body, as direct measurements show it to be at longer wavelengths, whether as some rocket observations suggest a great deal of additional radiation exists, or whether at wavelengths shorter than about 2 mm there is indeed any radiation at aU-a possibility that cannot be entirely discounted. Space does not allow review here of the theoretical speculations based on the possible existence of a large short-wavelength flux, and it is not clear that such a review is worthwhile until the observational situation described here is clarified (see Caroff & Petrosian 1971, and Burbidge 1971 for references). The remarkable theoretical prediction of the microwave background over twenty years ago, the peculiar failure of this prediction to stimulate any obser vational search, and the accidental discovery of the radiation in 1965, are well reviewed elsewhere (see Alpher, Gamow & Herman 1967; Dautcourt & Wallis 1968; Partridge 1969; Field 1969; Penzias 1972), and will only be briefly sum marized. Gamow and his co-workers, notably Alpher and Herman, while considering the question of cosmological element production, first recognized the dominant role of hot blackbody radiation in the early expanding universe, and first realized that a highly redshifted remnant of this radiation, its blackbody character intact, might still survive (Alpher, Bethe & Gamow 1948; Gamow 1948; see Alpher, Gamow & Herman 1967 for further references). On the basis of various assump tions (today mostly questionable) the temperature of the radiation at the present cosmological epoch was estimated to be 5-28°K (Alpher & Herman 1949,1950,