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This paper presents an extensive intercomparison and validation for the ozone (O3) product measured by the two Infrared Atmospheric Sounding Interferometers (IASIs) launched on board the MetOp-A and MetOp-B satellites in 2006 and in 2012 respectively. IASI O3 total columns and vertical profiles obtained from Fast Optimal Retrievals on Layers for IASI (FORLI) v20140922 software (running up until recently) are validated against independent observations during the period 2008–2014 on a global scale. On average for the period 2013–2014, IASI-A and IASI-B total ozone columns (TOCs) retrieved using FORLI are consistent, with IASI-B providing slightly lower values with a global difference of only 0.2?±?0.8?%. The comparison between IASI-A and IASI-B O3 vertical profiles shows differences within ±?2?% over the entire altitude range. Global validation results for 7 years of IASI TOCs from FORLI against the Global Ozone Monitoring Experiment-2 (GOME-2) launched on board MetOp-A and Brewer–Dobson data show that, on average, IASI overestimates the ultraviolet (UV) data by 5–6?% with the largest differences found in the southern high latitudes. The comparison with UV–visible SAOZ (Systeme d'Analyse par Observation Zenithale) measurements shows a mean bias between IASI and SAOZ TOCs of 2–4?% in the midlatitudes and tropics and 7?% at the polar circle. Part of the discrepancies found at high latitudes can be attributed to the limited information content in the observations due to low brightness temperatures. The comparison with ozonesonde vertical profiles (limited to 30?km) shows that on average IASI with FORLI processing underestimates O3 by ????5–15?% in the troposphere while it overestimates O3 by ???10–40?% in the stratosphere, depending on the latitude.