The Infrared Space Observatory (ISO) is an ESA (European Space Agency) project with instruments funded by ESA member states (especially the PI countries France, Germany, The Netherlands and the United Kingdom) and with participation of ISAS (Japan) and NASA (USA). It was operated from November 1995 till May 1998, almost a year longer than expected. As an unprecedented observatory for infrared astronomy, able to examine cool and hidden places in the Universe, ISO successfully made nearly 30,000 scientific observations. The ISO Data Archive is available at the ISO Data Centre at https://www.cosmos.esa.int/web/iso it includes about 150,000 observations, if account is taken of calibration and parallel or serendipity mode observations. The catalogue contains all observations performed in standard observing modes exempt from technical problems; special flags indicate calibration observations. ISO helpdesk: https://support.cosmos.esa.int/iso/