The book collections of the Library of Congress were reestablished, after their destruction in 1814, by the purchase of the private library of Thomas Jefferson (1743-1826), which was authorized on January 26, 1815, for the sum of $23,950. At the time of the purchase, Jefferson's collection contained 6,487 volumes in the fields of politics, history, science, law literature, fine arts, and philosophy and was recognized as one of the finest private libraries in the United States. While some members of Congress objected that the collection went beyond the subject areas of law and governance, Jefferson made the notable statement, "There is, in fact, no subject to which a member of Congress may not have occasion to refer," which is still the guiding principle for Library acquisitions.

Thomas Jefferson followed a modified version of an organizational system created by British philosopher Francis Bacon (1561–1626) to arrange the books in his library, then the largest private book collection in North America. Divided into categories of Memory, Reason, and Imagination—which Jefferson translated to “History,” “Philosophy,” and “Fine Arts”—and further divided into forty-four “chapters,” the collection placed at Jefferson’s fingertips the span of his multifaceted interests.

Accordingly, the Jefferson Library forms the nucleus around which the present collections of the Library of Congress have been assembled. For nearly a century the subject arrangement that Jefferson developed from Sir Francis Bacon's division of knowledge was used to organize the Library of Congress book collection, and the Library has continued to collect books on nearly every subject area by creators from all over the world.

While many of the Jefferson books were lost in the Library fire of 1851, the remaining volumes have been assembled as a unit in the Rare Book and Special Collections Division and are on permanent display in the Library's Great Hall. Many books bear Jefferson's ownership markings as well as the original Library of Congress bookplates and classification. The contents of the entire 1815 purchase were reconstructed by E. Millicent Sowerby and described in a five volume set which is now made available digitally.