A library designated and funded by a nation's government as a comprehensive collection of the published output of that nation and which serves the nation as a whole. The national library of the United States is the Library of Congress, located in Washington, D.C.
"National libraries have special responsibilities, often defined in law, within a nation's library and information system. These responsibilities vary from country to country but are likely to include: the collection via legal deposit (i.e., copyright) of the national imprint (both print and electronic) and its cataloguing (cataloging) and preservation; the provision of central services (e.g., reference, bibliography, preservation, lending) to users both directly and through other library and information centres (i.e., ILL); the preservation and promotion of the national cultural heritage; acquisition of at least a representative collection of foreign publications; the promotion of national cultural policy; and leadership in national literacy campaigns. National libraries often serve as a national forum for international programmes and projects. They may have a close relationship with national governments, may be concerned with the development of national information policies, and may act as a conduit for the views of other sectors of the profession. Occasionally they also serve the information needs of the legislature directly." -- International Federation of Library Associations and Institutions (IFLA), IFLA National Libraries Section