Helene Hanff (April 15, 1916–April 9, 1997) was an American writer. Born in Philadelphia, Pennsylvania, she is best known as the author of the book 84 Charing Cross Road, which became the basis for a play, teleplay, and film of the same name.

Her career, which saw her move from writing unproduced plays to helping create some of the earliest television dramas to becoming a kind of professional New Yorker, goes far beyond the charm of that one book. She called her 1961 memoir Underfoot in Show Business, and it chronicled the struggle of an ambitious young playwright to make it in the world of New York theatre in the 1940s and 1950s. She worked in publicists' offices and spent summers on the "straw hat" circuit along the East Coast of the United States, writing plays that were admired by some of Broadway's leading producers but which somehow never saw the light of day.

She wrote and edited scripts for a variety of early television dramas produced out of New York, all the while continuing to try and move from being what she called "one of the 999 out of 1,000 who don't become Noel Coward." When the bulk of television production moved to California, her work slowly dried up, and she turned to writing for magazines and, eventually, to the books that made her reputation.

First published in 1970, the epistolary work 84 Charing Cross Road chronicles her 20 years of correspondence with Frank Doel, the chief buyer for Marks & Co., a London bookshop, on which she depended for the obscure classics and British literature titles around which her passion for self-education revolved. She became intimately involved in the lives of the shop's staff, sending them food parcels during England's post-war shortages and sharing with them details of her life in Manhattan.

Due to financial difficulties and an aversion to travel, she put off visiting her English friends until too late; Doel died in December 1968 from peritonitis from a burst appendix, and the bookshop eventually closed. Hanff did finally visit Charing Cross Road and the empty but still standing shop in the summer of 1971, a trip recorded in her 1973 book The Duchess of Bloomsbury Street.

In the 1987 film of 84 Charing Cross Road (film), Hanff was played by Anne Bancroft, while Anthony Hopkins took the part of Frank Doel. Anne Jackson had earlier played Hanff in a 1975 adaptation of the book for British television. Ellen Burstyn recreated the role on Broadway in 1982 at the Nederlander Theater in New York City.

She later put her obsession with British scholar Sir Arthur Quiller-Couch to use in a book called Q's Legacy. Other books include Apple of My Eye, an idiosyncratic guide to New York City, and A Letter from New York (1992), which reprinted talks she gave on the BBC's Woman's Hour between 1978 and 1985.

Hanff was never shy about her fondness for cigarettes and martinis, but nevertheless lived to be 80, dying of diabetes in 1997 in New York City. The apartment building where she lived at 305 E. 72nd Street has been named "Charing Cross House" in her honor. A bronze plaque next to the front door commemorates her residence and authorship of the book.