ERA-Interim is the latest global atmospheric reanalysis, which was produced by the "European Centre for Medium Range Weather Forecasts" (ECMWF). The ERA-Interim-project was carried out inorder to replace the previous atmospheric reanalysis ERA-40. So far it dates back to 1979 and has been continued to the present. The forecast model, data assimilation method and input data sets for ERA-Interim are described in the articles mentioned in the references, where the performance of the system is discussed, too. Problems that occurred in ERA-40 have been treated with improved methods in this new reanalysis. The identified problems were the hydrological cycle, the quality of the stratospheric circulation, and the time consistency of the analyzed fields. The number of pressure levels from ERA-40 has been increased from 23 to 37 levels and additional cloud parameters are included. The use is now free for both scientific and commercial purposes.