This paper presents a summary of the mission -including some of its highlights- of the European Space Agency's (ESA) Infrared Space Observatory. ISO, the world's first true orbiting infrared observatory, was launched by Ariane in November 1995 and provided astronomers across the globe with a facility of unprecedented sensitivity and capabilities for a detailed exploration of the universe at infrared wavelengths (2.5-240 mum). Its 60 cm-diameter telescope was cooled by superfluid liquid helium to temperatures of 2-4 K and it was equipped with four highly-sophisticated and versatile scientific instruments. The mission was a great technical, operational and scientific success with most satellite systems operating far better than specifications and with its scientific results impacting practically all fields of astronomy. During its routine operational phase, which lasted until April 1998 almost a year longer than specified, ISO successfully made some 30000 individual imaging, photometric, spectroscopic and polarimetric observations ranging from objects in our own solar system right out to the most distant extragalactic sources. ISO's data archive, accessible via www.iso.vilspa.esa.es, opened to the community in December 1998 and, including data from calibration and auxiliary mode observations, contains about 100,000 data sets. (C) 2002 Published by Elsevier Science Ltd on behalf of COSPAR.
