The 20th Century Reanalysis version 2 (20CRV2) is an effort led by PSL and the CIRES at the University of Colorado to produce a reanalysis dataset spanning the entire twentieth century, assimilating only surface observations of synoptic pressure, monthly sea surface temperature and sea ice distribution. V1 was initially completed as a test from 1950-1958. V2 covers the period from 1871-2012 . The model used is a 2008 experimental, reduced-resolution version of the NCEP Global Forecast System (GFS2008ex). Briefly, that model has a spatial resolution of nearly 200-km on an irregular Gaussian grid in the horizontal (corresponding to a spherical harmonic representation of model fields truncated at total wavenumber 62, T62). In the vertical, we use finite differencing of 28 levels. The model has a complete suite of physical parameterizations as described in Kanamitsu et al. (1991) with updates detailed in Moorthi et al. (2001). Additional updates to these parameterizations are described in Saha et al. [Need YEAR] and include revised solar radiation transfer, boundary layer vertical diffusion, cumulus convection, and gravity wave drag parameterizations. In addition, the cloud liquid water is a prognostic quantity with a simple cloud microphysics parameterization. The radiation interacts with a fractional cloud cover that is diagnostically determined by the predicted cloud liquid water. The radiation also interacts with stratospheric ozone that is determined prognostically. The GFS2008ex also includes the radiative effects of historical time-varying CO2 concentrations, volcanic aerosol and solar variations using the longwave radiation model of Mlawer et al. (1997) and shortwave radiation model of Hou et al. (2002). Pressure observations are from the International Surface Pressure Databank station component version 2. It is run as an 56 member forecast ensemble. The boundary forcing is taken from the HadISST 1.1 (time-evolving sea-surface temperature and sea-ice). The model is run using 9 hour integrations of the ensemble members. A subset of the model variables are output every 6 hours. Additional variables are available every 3 hours. In addition to the subdaily values, the dataset also includes daily and monthly average values. In addition to the mean values, standard deviations of the 56 ensemble members are also provided for the subdaily and monthly average output. Subdaily, daily, and monthly long terms means of both the model means and standard deviations are also provided (1981-2010). Output includes 2D and 3D variables. The 3D atmospheric variables are on 24 pressure levels extending from 1000mb to 10mb. Soil moisture is provided on 4? levels. The horizontal resolution of the 2D and 3D variables are about 2 degrees latitude by 2 degrees longitude. Individual ensemble members are available via the NERSC interface https://portal.nersc.gov/project/20C_Reanalysis/. All data are in netCDF4 format. Total 20CRV2 data volume at PSL is approximately 4TB. In general, data is divided into annual files (except for monthly values). The files are available via FTP and OPEnDAP (THREDDS) and a selection of plotting and analysis tools.