Abstract The Space Infrared Telescope Facility (SIRTF) is to be launched by NASA in 2003. SIRTF will be an observatory for infrared astronomy from space with an 85 cm aperture telescope operating at 5.5 K and a 2.5–5 years cryogenic lifetime. SIRTFs three instruments with state of the art detector arrays will provide imaging, photometry, and spectroscopy over the 3–180 μm wavelength range. SIRTF will provide major advances for the study of astrophysical problems from the solar system to the edge of the Universe. SIRTF will complete NASA’s family of Great Observatories and serve as a cornerstone of the Origins program. Over 75% of the observing time will be awarded to the general scientific community through the usual proposal and peer review cycle. SIRTF will demonstrate major advances in technology areas critical to future infrared missions. These include lightweight cryogenic optics, sensitive detector arrays, and a high performance thermal system, combining radiative and cryogenic cooling, which allows the telescope to be launched warm and to cool in space. These thermal advances are enabled by the use of an Earth-trailing solar orbit which carries SIRTF to a distance of ∼0.6 AU from Earth in five years. SIRTF will be launched in April, 2003; thus, by the time this paper is published, SIRTF will be in orbit and returning data. Many more scientific and technical details can be found on the SIRTF home page: sirtf@caltech.edu/SSC/ ; this site will also alert the scientific community to upcoming research opportunities with SIRTF.