The Herschel space observatory is an ESA mission, with a participation from NASA and Canada. It operates in the infrared and submillimeter window, between 60 and 670 microns, in several photometric and spectroscopic observing modes. It is named after William Herschel, who in 1800 first discovered that the electromagnetic spectrum extended beyond the red, through the thermal effects of this invisible radiation. Herschel is the fourth of the large infrared space missions, after IRAS, ISO, and Spitzer. Its primary mirror of 3.5 m is the largest in space, and its detectors employ bolometer arrays also for the first time in space (simultaneously with Planck). Its sensitivity is mostly limited by the confusion noise from background sources, and not by instrumental noise or the atmospheric foreground. A major breakthrough is also achieved by the spectroscopic capabilities in the far-infrared, covering an extended wavelength range with a spectral resolution that can be very high. Herschel targets the cold universe, namely dust and gas at temperatures below a few hundred Kelvins. Such material is contained in astrophysical objects of all kinds: solar system bodies, protostars, young stars still embedded in cocoons, circumstellar disks and envelopes, the interstellar medium in galaxies, from the Milky Way to the distant universe, and the intergalactic medium as well. Observation programs address in particular these major scientific topics: the stellar formation process; the interstellar medium physics and chemistry, including matter and energy cycles; the evolution of galaxies from their formation epoch to the present time. Many european institutes are part of the consortia of the three instruments, HIFI, PACS, and SPIRE. IAP is in charge of both technical support (see the "Services d'observation" menu) and scientific exploitation. Several staff members are co-investigators or associates of some guaranteed-time and open-time observation programs (for more information, see the relevant pages of each research group).