We present a quasi three-dimensional ozone data set (Candidoz Assimilated Three-dimensional Ozone, CATO) with daily resolution and covering the period 1979–2004. It was reconstructed from two-dimensional total ozone observations of the Total Ozone Mapping Spectrometer (TOMS), Global Ozone Monitoring Experiment (GOME), and Solar Backscatter UV (SBUV) satellite instruments by assimilating the measurements into an equivalent latitude (ϕE)–potential temperature (θ) framework. The statistical reconstruction method uses the fact that total ozone columns are influenced by transient north-south excursions of air parcels associated, for instance, with Rossby waves. These adiabatic motions change the thickness of individual isentropic layers and transport high or low ozone into the column depending on meridional concentration gradients. A Kalman filter was employed to calculate sequentially the ozone distributions on a (ϕE, θ) grid that best match the total ozone observations given the errors in both the measurements and the ozone field predicted by the filter. CATO is shown to agree in midlatitudes within 20% with ozonesondes and the Halogen Occultation Experiment (HALOE) capturing both seasonal and interannual variations. Significantly larger differences of about 30% are found at the high-latitude sonde station Sodankylä (67°N), while differences from HALOE are mostly within 20% at these latitudes. Differences of about 30% from both the sondes and HALOE are found in the tropical lower stratosphere. This new data set is unique in its temporal and spatial coverage and will be particularly useful for studies of the factors influencing the long-term evolution of ozone in the lower stratosphere.