Heritage Documentation Programs (HDP) is part of the National Park Service. It administers the Historic American Buildings Survey (HABS), the Federal Government's oldest preservation program, and its companion programs: the Historic American Engineering Record (HAER) and the Historic American Landscapes Survey (HALS). Documentation produced through HABS/HAER/HALS constitutes the nation's largest archive of historic architectural, engineering, and landscape documentation. Records on more than 40,000 historic sites (consisting of large-format black and white photographs, measured drawings, and written historical reports) are maintained in a special collection at the Library of Congress, available to the public copyright free in both hard copy (at the Library of Congress) and via the Library's website. HDP also develops and maintains the Secretary of the Interior's Standards and Guidelines for Architectural and Engineering Documentation.

HDP conducts a nationwide documentation program in partnership with state and local governments, private industry, professional societies, universities, preservation groups, and other Federal agencies. The program assigns highest priority to sites that are in danger of demolition or loss by neglect, and to National Park Service properties. In addition to the summer recording program, documentation enters the Collection through mitigation activities under appropriate sections of the National Historic Preservation Act of 1966, submissions in prize competitions, and donations.

Documentation provides a permanent record of the nation's most important historic sites and large-scale objects. The Collection is unique in the strong support it enjoys from its institutional sponsors and the public, and is distinguished in its national scope, consistent format, archival stability, and continued growth. The documentation contributes to wider recognition and appreciation of historic resources as National Historic Landmarks, provides baseline documentation for rehabilitation and restoration, and makes available well-researched materials for interpretation and illustration. Unsurprisingly, it is the most heavily used collection at the Library of Congress' Division of Prints and Photographs.