Part of the abstract: The Michelson Interferometer for Passive AtmosphericSounding (MIPAS), on-board the European ENVIronmentalSATellite (ENVISAT) launched on 1 March 2002,is a middle infrared Fourier Transform spectrometer measuringthe atmospheric emission spectrum in limb sounding geometry.The instrument is capable to retrieve the vertical distributionMIPAS data were re-processed by ESA using updated versions ofthe Instrument Processing Facility (IPF v4.61 and v4.62) andprovided a complete set of level-2 operational products (geolocatedvertical profiles of temperature and volume mixingratio of H2O, O3, HNO3, CH4, N2O and NO2). MIPAS operated in its standard observation mode for approximately two years, from July 2002 to March 2004. MIPAS data were re-processed by ESA using updated versions of the Instrument Processing Facility (IPF v4.61 and v4.62) and provided a complete set of level-2 operational products (geolocated vertical profiles of temperature and volume mixing ratio of H2O, O3, HNO3, CH4, N2O and NO2). MIPAS operated in its standard observation mode from July 2002 to March 2004, covering the altitude range from the mesosphere to the upper troposphere with relatively high vertical resolution (about 3 km in the stratosphere). In this paper, we report a detailed description of the validation of MIPAS-ENVISAT operational ozone data, that was based on the comparison between MIPAS v4.61 (and, to a lesser extent, v4.62) O3 VMR profilesand a comprehensive set of correlative data, including observations from ozone sondes, ground-based lidar, FTIR and microwave radiometers, remote-sensing and in situ instruments on-board stratospheric aircraft and balloons, concurrent satellite sensors and ozone fields assimilated by theEuropean Center for Medium-range Weather Forecasting. A clear indication of the validity of MIPAS O3 vertical profiles is obtained for most of the stratosphere, where the mean relative difference with the individual correlative data sets is always lower than ±10%. Furthermore, these differences always fall within the combined systematic error (from1 hPa to 50 hPa) and the standard deviation is fully consistent with the random error of the comparison (from 1 hPa to 3040 hPa).