William J. Lynn III served as the 30th Deputy Secretary of Defense from February 12, 2009 until October 5, 2011.

The Deputy Secretary of Defense is the second-highest-ranking official in the Department of Defense of the United States of America.  The Deputy Secretary is the principal civilian deputy to the Secretary of Defense, and is appointed by the President, with the advice and consent of the Senate.  The Deputy Secretary, by statute, must be a civilian, at least seven years removed from service as a commissioned officer on active-duty at the date of appointment.