Constance Elaine Trimmer Willis is an American science fiction writer. She has won eleven Hugo Awards and seven Nebula Awards for particular works —more "major awards" than any other writer— most recently the year's "Best Novel" Hugo and Nebula Awards for Blackout/All Clear. She was inducted by the Science Fiction Hall of Fame in 2009 and the Science Fiction Writers of America named her its 28th SFWA Grand Master in 2011.
Several of her works feature time travel by history students at a faculty of the future University of Oxford—sometimes called the Time Travel series. They are the short story "Fire Watch", the novels Doomsday Book and To Say Nothing of the Dog, as well as the two-part novel Blackout/All Clear. All four won the annual Hugo Award and all but To Say Nothing of the Dog won both the Hugo and Nebula Awards.