Aerosol radiative forcing is a major unknown in climate modelling. Owing to the large spatial and temporal variability exhibited by atmospheric aerosol concentrations remote sensing is the only feasible way to obtain global measurements. The ATSR-2 (1995–2002) and AATSR (2002-) radiometer instruments together provide one of the longest available, well calibrated datasets of satellite radiance measurements. The algorithm presented here enables the retrieval of aerosol optical depths (AODs) from these data over a wide variety of surface types including ocean, vegetated land surfaces, and desert. This paper demonstrates the potential for retrievals based on ATSR-2 and AATSR data to reveal spatial and temporal signals in AOD from 1995 onwards. AODs based on AATSR data are validated against surface-based measurements and 6-year time series of regional monthly composites are presented.