The CCI/C3S level-2 total ozone Essential Climate Variable product contains harmonized total ozone vertical column densities retrieved from a number of nadir space sensors. The present data set provides ozone total columns as well geophysical information for ground pixels observed by the Global Ozone Monitoring Experiment (GOME, aboard the ERS-2 satellite; descending node equator crossing time: circa 10:30 hrs local time) for the period June 1995 - July 2011. The product also contains diagnostic metrics such as the results of the spectral fit, averaging kernel, a priori profiles, cloud information, and algorithm and product uncertainty estimates.