Library of Congress Subject Headings (LCSH) has been maintained since 1898 to catalog materials held at the national library. With cooperative cataloging, other libraries also use LCSH to provide subject access to their collections. 

Library of Congress Classification Outline, the letters and titles of the main classes of the national library's arrangement of materials.

Historical research is often informed by reference materials from many disciplines. Reference online and in print brings together some of the library's many reference works while providing tips on how to locate others.  The types of works profiled in this guide include dictionaries, encyclopedias, thesauri, grammar and usage guides, biographical sources, sources for quick facts, directories and bibliographies, across the disciplines.  

Reference resources come in several formats.  Online resources will be shown by title in NUsearch.  Print resources are also listed in NUsearch, by title.  Print resources which do not circulate are available in the main library periodical room.  For more information, send us an IM, email or call us.