The objectives of the European Centre for Medium-Range Weather Forecasts ERA-Interim project are to produce and promote use of a comprehensive set of global analyses describing the state of the atmosphere, land and ocean-wave conditions from 1979 to present. The ERA-Interim project builds on the previous work undertaken by the ERA-15 and ERA-40 projects. ERA-Interim is continuously updated in real time at ECMWF, though products are later processed before delivery to the BADC. The data assimilation system used to produce ERA-Interim is based on a 2006 release of the IFS (Cy31r2). The system includes a 4-dimensional variational analysis (4D-Var) with a 12-hour analysis window. The spatial resolution of the data set is approximately 80 km (T255 spectral) on 60 vertical levels from the surface up to 0.1 hPa. An open-access journal article describing the ERA-Interim reanalysis is available from the Quarterly Journal of the Royal Meteorological Society. Additional details of the modeling and data assimilation system used to produce ERA-Interim can be found in the IFS Cy31r1 documentation.