Constance Elaine Trimmer Willis (born 31 December 1945) is an American science fiction writer. She has won eleven Hugo Awards and seven Nebula Awards. Willis most recently won a Hugo Award for Blackout/All Clear (August 2011). She was inducted to the Science Fiction Museum and Science Fiction Hall of Fame in 2009.
Willis's first published story, "The Secret of Santa Titicaca," appeared in Worlds of Fantasy in 1971. After receiving an NEA grant in 1982, she left her teaching job and became a full-time writer.
Willis is known for her accessible prose and likable characters. She has written several pieces involving time travel by history students and faculty of the future University of Oxford. These pieces include her Hugo Award-winning novels Doomsday Book and To Say Nothing of the Dog, the short story "Fire Watch" (found in the short story collection of the same name), and the two-volume novel Blackout/All Clear. All but one of the Oxford University Time Travel tales have won both the Hugo Award and the Nebula Award.