In the arid regions of the western United States plant macrofossil assemblages from packrat middens are among the best sources of information on late Pleistocene and Holocene vegetation changes. Unfortunately, many different methods have been used to collect and analyze midden data, which makes it difficult to compare data and conduct analyses utilizing data from different sources. The USGS/NOAA North American Packrat Midden Database is a joint project developed by the U.S. Geological Survey and National Oceanic and Atmospheric Administration with the purpose to provide researchers with access to standardized midden data that can be useful for investigating late Quaternary changes in plant species distributions in response to climate and environmental change. The database currently contains original data from more than 1000 packrat midden samples collected from over 200 caves or rock shelters ranging from Montana to northern Mexico. The database includes locality information, radiocarbon ages, and lists of plant macrofossil taxa (over 1100 searchable taxa) from 76 published and unpublished sources. Data were entered into a Microsoft Access database with the intent to preserve the data in the original format used by each investigator. To facilitate the comparison and use of data from different sources, the database translates original species relative abundance data into a simplified uniform format. Similarly, the taxonomic usage of the original authors is preserved, but a uniform approach to current taxonomy is also presented. The USGS/NOAA North American Packrat Midden Database can be accessed via the Internet at http://climchange.cr.usgs.gov/data/midden/.