This paper describes the scientific and technical background and prospects for the Space Infrared Telescope Facility (SIRTF). SIRTF is a cryogenically-cooled, one meter-class space telescope which will be operated by NASA as an observatory for infrared astronomy, in the mid-1990's. SIRTF will build on the scientific and technical success of IRAS, but will have greater capabilities in all important scientific areas - wavelength coverage, spectral and spatial resolution, and sensitivity. SIRTF will provide detailed studies of even the faintest IRAS sources, important new capabilities for the study of known astrophysical phenomena, and the potential to make new and unexpected discoveries about the nature of the Universe. SIRTF will be a long-life observatory and will support a vigorous general investigator program accessible to the international scientific community. The long-life SIRTF mission has undergone intensive review by the SIRTF Science Working Group, which was selected in mid-1984. In this paper, we present the outcome of that review process and describe the SIRTF program as it is now envisioned. Particular emphasis will be placed on the choice of orbit for SIRTF, the SIRTF scientific performance requirements and the baseline design concept for the SIRTF facility and mission.