Library of Congress >> About the Library >> Especially for Researchers
Closed Stack System
The enormous size and variety of its collections make the Library of Congress the largest library in the world. Comprised of approximately 130 million items in virtually all formats, languages, and subjects, these collections are the single most comprehensive accumulation of human expression ever assembled. The collections are broad in scope, including research materials in more than 460 languages and in many formats and media.
Most of the Library's collections are housed in closed stack areas within the three Library buildings on Capitol Hill. Researchers do not have direct access to the closed stack areas of the collections and must submit requests for materials from those areas. In order to identify what is desired and what the Library has, patrons consult the Library's online and card catalogs, reference sources, and reference librarians. Once materials are identified, researchers submit online or manual request slips. Requested materials that are available are then delivered to requesters at desks in the various reading rooms or are kept in holding areas for later pickup. Delivery times vary from one reading room to another, and retrieval of materials may frequently take as long as 60 to 90 minutes. For materials stored at a location other than one of the Capitol Hill buildings, delivery times can stretch to 24 hours or more. For more information about the delivery times in a particular reading room, one should contact that reading room.
If materials are not available, researchers in many cases are able to initiate special searches. Materials may not be available for a variety of reasons: loans to other libraries or for exhibits; in use by members and staff of Congress; in use by other researchers or staff; or undergoing preservation treatment. For special search services in a particular reading room, inquire with the staff in that location.
All of the Library of Congress public reading rooms also maintain open stack collections of reference materials (encyclopedias, periodical indexes, biographical guides, etc.) that relate to their subject or topic or language and area study expertise. These reference collections may be consulted directly without submitting a request slip.