The Smithsonian Astrophysical Observatory (SAO) was established in 1890 as research unit of the Smithsonian Institution concentrating on studies of solar radiance. Sixty-five years later, SAO assumed responsibility for establishing an optical network for tracking the first artificial satellites. From this pioneering effort, the size and scope of SAO grew with the international space program to include major research in virtually all branches of astrophysics, as well as in areas of earth and planetary sciences. Since 1955, when its headquarters moved to Cambridge, Massachusetts, SAO has pursued such research in close collaboration with the Harvard College Observatory (HCO) and Harvard University Department of Astronomy. On July 1, 1973, the Smithsonian Institution and Harvard University formalized their collaboration now known as the Center for Astrophysics | Harvard & Smithsonian (CfA) to coordinate the related research activities of the two observatories under a single director. Today the observatories retain their separate identities, each responsible to its parent organization; however, the joint venture draws on the coordinated strengths of the two organizations and the combined staffs in six research divisions: Atomic and Molecular Physics; High Energy Astrophysics; Optical and Infrared Astronomy; Radio and Geoastronomy; Solar, Stellar, and Planetary Sciences; and Theoretical Astrophysics. In addition, the CfA has a Science Education Department.