The UGAMP ozone climatology consists in a 4-dimensional distribution of ozone that has been built up from the combination of several observational data sets. These data sets include satellite observations (SBUV, SAGE II, SME, TOMS) as well as ozone sonde data provided by the Atmospheric Environment Service of Canada. This global climatology, covering five years (1985 to 1989), was originally established to replace the simpler ozone climatologies used as input in the UGAMP models (ECMWF parameterization or 2-D zonal means deduced from satellite data). It provides monthly means of the ozone column above the grid levels as well as 5-year averages and zonal averages of these monthly means, on a 2.5 x 2.5 deg horizontal grid and over 47 levels, from the ground up to 0.001 mb. Software to convert ozone columns into mixing ratio and to interpolate the data on any required grid is also available.