Antonia Susan Byatt (born August 24, 1936, Sheffield, England) has been hailed by some as one of the greatest postmodern novelists in Britain. She is usually known as A. S. Byatt.

She was educated at the University of Cambridge, before teaching at the University of London and the Central School of Art and Design. Her younger half-sister, Margaret Drabble, is also a successful novelist, and the rivalry between the two is legendary, although of uncertain origin. It has been suggested by some that, before becoming successful in her own right, Byatt resented her sister. Drabble herself suggests that part of the rift is due, after the death of Byatt's son in a car accident, to the guilt she felt that her own children survived (this reported by Suzie Mackenzie of the U.K.'s Guardian Unlimited.) Byatt has stated publicly that Drabble's depiction of their mother in Drabble's book The Peppered Moth angered her.

Since becoming a full-time writer, Byatt has published several novels, including Possession which won the prestigious Booker Prize in 1990.

More recently, A. S. Byatt caused controversy by suggesting that the popularity of J. K. Rowling's Harry Potter series of books is because they are "written for people whose imaginative lives are confined to TV cartoons, and the exaggerated (more exciting, not threatening) mirror-worlds of soaps, reality TV and celebrity gossip." In her editorial column in the New York Times newspaper, she scathingly attacked adult readers of the series as uncultured, claiming that "they don't have the skills to tell ersatz magic from the real thing, for as children they daily invested the ersatz with what imagination they had."

After the column appeared in the newspaper, her editorial was described by Salon.com contributing writer Charles Taylor as "upfront in its snobbishness." He also suggested that Byatt's claims may be due to jealousy towards Rowling's commercial success, though given her vigorous defence of the novels of Terry Pratchett against mid-brow pundits this criticism seems particularly ill-founded.

Also well-known for her short stories, Byatt is allegedly influenced by Henry James and George Eliot as well as Emily Dickinson, T. S. Eliot, and Robert Browning, as she merges realism and naturalism with the fantasies of Victorian literature. Byatt prefers to offer fantasy not as an escape, but as an alternative to, everyday life, creating what is often termed a "hybrid genre", a combination of experimental and realistic work.

Two of her works have been adapted into motion pictures: Possession and Angels & Insects.