To request a book or periodical from the General Collections of the Library of Congress, you will need to locate the Call Number assigned to the item. Call Numbers (which designate a shelving location for each item) are composed using LC Classification (LCC). 

The multivolume Library of Congress Classification (Washington: Library of Congress, Cataloging Distribution Service, [irregular]; Z696.U5 MRR Ref Desk) shows the full range of Library call numbers. The LCC Outline is available online from the Library's Acquisitions and Bibliographic Access Directorate.

These unique numbers are composed of one, two, or three letters followed by a combination of numbers and letters. For example, call numbers for many books on medicine begin with R; the range for gynecology and obstetrics is RG1-991, and for nursing, it is RT1-120. Call numbers for bibliographies begin with Z; many bibliographies on women have numbers between Z7961 and Z7965, and those specifically on the employment of women are-Z7963.E7. But some bibliographies on African American women are in Z1361.N39. This last instance shows that you must be very cautious when searching for a subject by call numbers, for they are as specific as subject headings. Bibliographies solely on women usually have a different call number from those on both men and women. Bibliographies on women belonging to a specific racial, religious, or ethnic group may have a number different from the general one for “women.” Nonetheless, when used carefully, this grouping by subject makes browsing the online catalog by call number another worthwhile way to search for items on a specific topic.

With the first part of a call number, you can scan the online records for books and bound periodicals in the order in which the volumes sit on the shelves, thereby coming close to “browsing the stacks” in the Library of Congress. Call-number searching is especially helpful for older works that received only very broad subject headings, such as “Girls” or “Conduct of life,” and for works that have no subject terms at all in the online catalog. 

Call numbers for collection items are provided in the text or in the notes for this guide. Some sections conclude with a few examples of Library of Congress call numbers to aid in searching. Subject searching by call number works best for books and periodicals since some of the special-format collections in the Library use other call number or shelving systems that may bear little relationship to the content of the collection.