David Mao has been appointed law librarian of Congress, the 23rd in history to hold the post.

Library of Congress head James Billington announced the appointment, effective immediately, in a statement this afternoon.

“Mr. Mao … has shown the ability to think strategically and work with external constituencies to advance the progress of the Law Library,” Billington said of Mao, who has served as deputy law librarian since 2010. “He will continue and expand upon the strides made in the past two years in clearly identifying priorities and setting the future course of the Law Library of Congress.”

Before joining the Law Library in 2010, Mao worked for the Congressional Research Service for five years. He also held positions at Georgetown University and the law firm Covington & Burling.

Mao succeeds Roberta Shaffer, whom Billington appointed as associate librarian for library services today.

Shaffer had served as the law librarian of Congress since August 2009 and was previously the executive director of the Federal Library and Information Center Committee and the Federal Library Information Network.