Spectra and spectroheliograms of prominences have been obtained at wavelengths of 300 to 1400 A from instruments aboard the OSO 4 and OSO 6 spacecraft. Quiescent prominences appear in emission above the limb for all strong lines formed at temperatures below 300,000 K, but not at higher temperatures. The gas pressure in the 100,000-K transition zone around prominences is approximately equal to that in the cooler (6500 K) central regions. The temperature and the hydrogen ground-state departure coefficient in the central regions are determined from the Lyman-continuum spectrum. Prominences on the disk (filaments) are visible in absorption in many lines, especially those at wavelengths below the hydrogen Lyman limit at 912 A.