The Infrared Space Observatory (ISO), a fully approved and funded project of the European Space Agency (ESA), will operate at wavelengths from 2.5 to 200 μm. The ISO will provide astronomers with a unique facility of unprecedented sensitivity for a detailed exploration of the universe ranging from objects in the solar system right out to the most distant extragalactic sources. The satellite essentially consists of a large liquid-helium cryostat, a telescope with a 60-cm-diam primary mirror, and four scientific instruments. The instrument complement is: an imaging photopolarimeter (2.5 to 200 μm), a camera (2.5 to 17 μm), a short-wavelength spectrometer (2.5 to 45 μm), and a long-wavelength spectrometer (45 to 180 μm). These instruments are being built by international consortia of scientific institutes and will be delivered to ESA for in-orbit operations. The ISO is scheduled to be launched in 1995 and will be operational for at least 18 months. In keeping with the ISO's role as an observatory, two-thirds of its observing time will be made available to the general astronomical community.