During Tony Hollingsworth's tenure as its Head of Research, ECMWF produced two widely-used atmospheric reanalyses, ERA-15 and ERA-40, and laid the seeds for a third, ERA-Interim. The improvements seen from one reanalysis to the next stem from many changes made to the underlying data assimilation system developed for operational weather prediction. An account will be given of the progress of these reanalysis activities, with emphasis placed on the more recent results from ERA-Interim, which runs from 1989 onwards. The presentation will cover the evolution of the accuracy of forecasts, the depiction of low-frequency variations and trends, and the related performance of the variational bias-correction scheme applied to the assimilation of radiance data from satellites.