The National Historical Geographic Information System (NHGIS) provides researchers and students interested in studying changes over time access to "population, housing, agricultural, and economic data, along with GIS-compatible boundary files, for geographic units in the United States from 1790 to the present." Visitors to this well-organized and regularly updated resource can use its data finder to filter by geographic levels, years, topics, and datasets, then download their selected data in one request. NGHIS also provides a number of helpful user resources, such as a user's guide, a thorough FAQ section, and a link to a user forum, to assist users in accessing and using the data. Also included is extensive documentation of summary tables, GIS files, and time series tables contained in this database. NHGIS is a data integration project of the Integrated Public Use Microdata Series (IPUMS), which is part of the Minnesota Population Center at the University of Minnesota, and it is funded by grants from the National Science Foundation and the National Institute of Child Health and Human Development.