David Chambers Mearns (December 31, 1899 – May 21, 1981) was a librarian and scholar of Abraham Lincoln. He held multiple positions at the Library of Congress over 58 years of service, including director of the reference department, chief of the manuscript division, and Chair of American History. Mearns wrote the first authoritative book on the Library's collection of Lincoln's papers, along with twelve other books. Librarian of Congress Archibald MacLeish described Mearns as "the rarest treasure in the Library of Congress".