| March 1979 | Proposal to ESA for ISO |
| 1979 | Assessment Study |
| 1980 | Pre-Phase-A Study |
| 1981-1982 | Phase-A Study |
| March 1983 | Selection of ISO for inclusion in ESA Scientific Programme |
| July 1984 | Call for Experiment and Mission Scientist Proposals |
| June 1985 | Selection of Scientific Instruments |
| December 1986 | Start of Phase-B (Definition) |
| March 1988 | Start of Phase-C/D (Main development) |
| April 1994 | Call for Observing Proposals |
| 17 November 1995 | Launch |
| 21 November 1995 | Start of Commissioning Phase |
| 9 December 1995 | Start of Performance Verification Phase |
| 4 February 1996 | Start of Routine Phase |
| August 1996 | Supplemental Call for Observing Proposals |
| February-July 1998 | Transition Phase to Post-Operations |
| 8 April 1998 | Helium boil-off / End of Routine Phase |
| 16 May 1998 | Termination of satellite communication |
| 9 December 1998 | Opening of the ISO Data Archive |
| August 1998-December 2001 | Post-Operations Phase |
| 28 February 2002 | Release of the ISO Legacy Archive |
| January 2002-December 2006 | Active Archive Phase |