The NOAA/National Severe Storms Laboratory Historical Weather Data Archives (NSSL HWDA) is a new web-based data portal that delivers surface and upper-air data to the online user through horizontal maps, vertical profiles on SkewT–logp charts, time series, and ASCII data listings. The data are primarily from the United States and Canada, but some worldwide data are available, especially after 1998 for surface data and 2000 for upper-air data. The surface data come primarily from the merger of two datasets from the NOAA/National Climatic Data Center (TD-3280 and DATSAV2) and are most complete from 1973 to 2003. The upper-air data come from the North American Radiosonde database and are most complete from 1946 to 2003. This article discusses the datasets, software, and capabilities of the NSSL HWDA. Future opportunities for improvements and additions to the NSSL HWDA are also described.