Margaret Peterson Haddix is an American writer known best for her children's series, Shadow Children (1998–2006) and The Missing (2008–2015). She also contributed to the multiple-author series, The 39 Clues.

Haddix grew up on a farm near Washington Court House, Ohio. She graduated from Miami University (of Ohio) with degrees in English/journalism, English/creative writing, and history. Before her first book was published, she worked as a newspaper copy editor in Fort Wayne, Indiana; a newspaper reporter in Indianapolis; and a community college instructor and freelance writer in Danville, Illinois.

She has since written more than 25 books for kids and teens, including Running Out of Time; Don’t You Dare Read This, Mrs. Dunphrey; Leaving Fishers; Just Ella; Turnabout; Takeoffs and Landings; The Girl with 500 Middle Names; Because of Anya; Escape from Memory; Say What?; The House on the Gulf; Double Identity; Dexter the Tough; and Up.