David Mao is an American law librarian. Mao served as acting Librarian of Congress from September 30, 2015, until the confirmation of Carla Hayden in 2016.

The librarian of Congress is the head of the Library of Congress, appointed by the president of the United States with the advice and consent of the United States Senate, for a term of ten years. The librarian of Congress also appoints and oversees the Register of Copyrights of the U.S. Copyright Office and has broad responsibilities around copyright, extending to electronic resources and fair use provisions outlined in the Digital Millennium Copyright Act. The librarian determines whether particular works are subject to DMCA prohibitions regarding technological access protection. In addition, the librarian appoints the U.S. poet laureate and awards the Gershwin Prize for Popular Song.