OAO-Copernicus, launched August 21, 1972, is in its third year of successful operation. Its contributions to scientific knowledge are contained in over 37 scientific papers. Princeton University Observatory has expanded the Guest Investigator Program to include 56 programs by a total of 66 astronomers from 23 countries. Observing time is currently scheduled for twelve months in advance. The engineering features of the Perkin-Elmer-built telescope are surveyed in this paper. A digest of the scientific results and a bibliography of OAO-C related papers is given, and the nature of the investigations planned at the time of writing (September 1974) is summarized.