The impact of Argo on ECMWF operational ocean analyses has been assessed by conducting a set of observing system experiments spanning the period 2001-2006. The experiments evaluate the information content of Argo temperature and salinity data, gauged in terms of influence on the ocean state and the skill of seasonal forecasts. The salinity data from Argo is instrumental in correcting the salinity of the ECMWF analysis on a basin-wide scale. The effect of Argo temperature is noticeable in the Indian, Atlantic and Southern Oceans. In the Pacific, the impact is modest, being confined to the South American coast. The information content of Argo combines well with the altimeter information in most regions. The impact of Argo on seasonal forecasts of sea surface temperature has been assessed for the period 2001-2006. The assimilation of Argo improves seasonal forecast skill in most areas, although the reduction of the error is small.