Sheila Marie Evans Widnall is an American aerospace researcher and Institute Professor Emerita at the Massachusetts Institute of Technology (MIT). She served as the United States Secretary of the Air Force from 1993 to 1997, becoming the first woman to hold that post and the first woman to lead an entire branch of the United States Armed Forces in the Department of Defense. She was elected to the National Academy of Engineering and the American Academy of Arts and Sciences and inducted into the National Women's Hall of Fame.