Frequently Asked Questions: General

The Library of Congress acquires materials from all over the world in many different formats, in hundreds of languages, and in diverse subject areas. Materials enter the Library through six primary sources (each source is linked to fuller information online):

• Purchase
• Copyright deposit
• Exchange
• Donation or gift
• Cataloging in Publication (CIP) and Preassigned Card Number (PCN) programs
• Transfer between federal government agencies

What We Collect

Although the Library of Congress is the largest library in the world, it does not have a copy of every item ever published, nor does it retain copies of every item submitted through the acquisition sources listed above for its research collection. The Library's permanent collections are shaped by Collections Policy Statements, with technical agricultural works acquired mainly by the National Agricultural Library and clinical medical works by the National Library of Medicine.

Special Collections and Finding Aids

In addition, many items from the Library's special collections are not represented by individual entries in the Library's Catalog. These materials are instead described in aggregated records. Catalog records for many archival collections are also linked to more detailed Finding Aids. Specialized online catalogs provide access to prints and photographs, historic newspapers, audio recordings, and more.

Databases and Other Catalogs

Databases, ejournals, and ebooks (including items found in fee-based online services) are generally accessible onsite, in one of the Library's reading rooms, often through the Library's E-Resources Online Catalog. Records for works registered with the Copyright Office after 1978 are searchable in the Copyright Catalog. Card entries for some items cataloged before 1980 are only available to researchers onsite in the Library's Main Card Catalog.