How Green Was My Valley is a novel of 1939, by Richard Llewellyn. The author's claims to have based it on his own knowledge of the Gilfach Goch area were bogus, as Llewellyn was English-born and spent little time in Wales, but gathered his facts from conversations with local mining families. The title of this heavily sentimentalised novel is taken from its last sentence: How green was my valley then, and the valley of them that have gone.

The novel tells the story of the Morgans, a poor but respectable mining family of the South Wales valleys, through the eyes of the youngest son, Huw Morgan. Huw's academic ability sets him apart from his elder brothers and enables him to consider a future away from this troubled industrial environment. His four brothers and his father are miners; after the eldest brother, Ifor, is killed in an industrial accident , Huw moves in with his sister-in-law, Bronwen, with whom he is secretly in love. Later, Huw's father is also killed in the mine. Meanwhile, Huw's only sister, Angharad, catches the eye of a wealthy coal-owner, but the marriage is an unhappy one and she enters into a clandestine relationship with the local minister. The death of Huw's father, coupled with the realisation that Bronwen has no romantic interest in him, causes him to leave the valley. In the sequels to the novel, Huw emigrates and makes a new life in Patagonia.

The immensely successful 1941 film of the book had a cast which included Walter Pidgeon, Maureen O'Hara, Anna Lee, Roddy McDowall (as Huw), and Barry Fitzgerald. None of the leading players were Welsh.

The film won five Oscars:

• Academy Award for Best Picture - Darryl F. Zanuck, producer
• Academy Award for Best Supporting Actor - Donald Crisp
• Academy Award for Best Art Direction-Interior Decoration, Black-and-White - Richard Day , Nathan Juran , and Thomas Little
• Academy Award for Best Cinematography, Black-and-White - Arthur C. Miller
• Academy Award for Directing - John Ford

It was also nominated for another five awards

• Academy Award for Best Supporting Actress - Sara Allgood
• Best Film Editing - James B. Clark
• Best Music, Scoring of a Dramatic Picture - Alfred Newman
• Best Sound, Recording - Edmund H. Hansen
• Best Writing, Screenplay - Philip Dunne

The 1939 version has been selected for preservation in the United States National Film Registry.

The book was successfully adapted for television during the 1970s by the BBC, with a script by Elaine Morgan. It starred Stanley Baker, Sian Phillips and Nerys Hughes .