The Architecture, Design, and Engineering category covers about 40,000 drawings (described in more than 3,900 catalog records), spanning 1600 to 1989, with most dating between 1880 and 1940. The designs are primarily for sites and structures in the U.S. (especially Washington, D.C.), as well as Europe and Mexico. American architects and architectural firms created most of the images. Building types range from the United States Capitol and the Library of Congress to private residences and hamburger restaurants.

Works by distinguished figures in the history of architecture, design, and engineering in the United States are well represented including Benjamin Henry Latrobe, William Thornton, Stephen Hallet, Thomas Ustick Walter, Montgomery C. Meigs, Cass Gilbert, and Frank Lloyd Wright. Extensive archives are available for Donald H. Drayer, Arthur B. Heaton, Iron Craftsmen, A.B. Mullett & Co., Waggaman & Ray, and Waddy B. Wood. The Library of Congress Prints & Photographs Division acquired these drawings chiefly through donations and continues to add new material.

Because of the fragility of the material and the time needed to prepare them for service, original drawings are served by advance appointment.