Libraries collect and preserve the graphic records of human experience.¹ Not every experience is documented, and not every documented experience is collected and preserved. How, then, can you know what part of the historical record remains for you to study? Reference sources are your map to the graphic records of human experience.

Even if every human experience hasn't been documented, and every document hasn't been preserved, there remains a plethora of sources available for the historian to study. Here at the University of Illinois Library, you have access to over 14 million printed books, 9 million microforms, 120,000 periodicals, 148,000 sound recordings, 1 million audiovisual resources, 280,000 e-books, 29,000 cubic feet of archival records, 3 terabytes of electronic records, and 650,000 maps—that's over 24 million potential primary sources for your research. Reference sources are your map to the Library's collections.

The role of the encyclopedia in library research is to summarize the established state of knowledge in a field of inquiry. An encyclopedia entry is like a digest of the secondary sources on a topic, but rarely reflects the most recent developments in scholarship. Encyclopedia entries will often include recommendations for further reading on the topic.

For history students, encyclopedias serve another important function: they help to verify that a particular topic already forms part of scholarly discourse, and they indicate that the topic, or some subset of it, can likely be researched using the kinds of published sources you will likely find in a library. Because encyclopedias summarize the secondary literature on a topic, they can help you identify dominant historical narratives.

Three online reference collections that students often find useful are:

A bibliography is, in its most literal sense, a list of books. Many students are familiar with bibliographies from writing research papers, where a list of works cited is sometimes called a bibliography. In libraries, bibliographies serve an additional, important function in helping patrons identify books, journal articles, and other library resources. These bibliographies are usually centered on sources about a particular subject, and are often book-length themselves. Some bibliographies run to several volumes. For more information on bibliographies, please see our guide to Bibliography and Historical Research:

A catalog is similar to a bibliography with the difference being that a catalog lists books and other resources available for use or purchase at a specific place, or from a specific person or organization. Examples are library catalogs, catalogs of private collections, and booksellers' catalogs.

Some catalogs and bibliographies are contemporaneous to the documents they list (see, for example, Labor under the New Deal), and these can be especially useful for identifying primary sources.

Guides (sometimes called "handbooks") can be almost anything. At worst, they are collections of articles on a subject (the Cambridge Guides, Blackwell Guides, and Oxford Handbooks tend to be of this type), at best they will combine elements of other reference sources, like encyclopedias, almanacs, chronologies, historiographical essays, and bibliographies.

A lot of biographical information can be easily obtained using a simple Google search. The biographical encyclopedias listed here are standard library reference works--old war horses if you want to call them that. Like the other encyclopedias on this page, they are tertiary sources

The most common reference sources of factual information are almanacs, chronologies, and statistical abstracts. Increasingly, databases make it possible to interact with large statistical datasets that until recently would have been possible only with advanced training. Even with the ability to manipulate statistical datasets, it's important to remember that interpreting statistics still requires specialized knowledge, which is why reference sources like statistical abstracts remain important to researchers without that advanced training.

1. Jesse H. Shera, The Foundations of Education for Librarianship (New York: Becker and Hayes, 1972): 193.