What follows is a scheme that tries to identify the writers, the time they worked on the film's screenplay, and their lasting contribution, if any.
- William H. Cannon (26 February 1938) — he wrote a four-page treatment that was not used
- Herman J. Mankiewicz (28 February to 23 March) — the Kansas sequence to be in black and white and the Oz scenes in color
- Noel Langley (11 March to 10 June, and later) — major portions of the end result, including Oz as a dream
- Irving Brecher, Robert Pirosh, and George Seaton (March)
- Ogden Nash (March/April) — his four-page treatment, dated 16 April, is in the collection of Arthur Freed's papers
- Herbert Fields (19 to 22 April)
- Samuel Hoffenstein (31 May to 3 June) — a two-page outline
- Florence Ryerson and Edgar Allan Woolf (4 June to 27 July) — multiple roles for the actor portraying the Wizard; Prof. Marvel; "There's no place like home" ending
- Noel Langley, again (30 July and after) — reversed some but not all of the Ryerson/Woolf changes
- E.Y. Harburg (Summer/Autumn) — the film's lyricist also polished the script, provided dialogue segues to the songs, and wrote the Wizard's speech about brains, heart, and courage
- Jack Mintz (3 August to 2 September) — contributed some jokes
- Sid Silvers (17 to 22 October) — Richard Thorpe's script doctor
- John Lee Mahin (27 October 1938 to 10 January 1939) — working closely with director Victor Fleming, he gave the script its final form. (The main screenwriters, Langley and the Ryerson/Woolf team, had added new characters and subplots that were subsequently cut away again.)
Hollywood studios sometimes had different writers or teams of writers work on the same project, simultaneously and independently. In early 1938, Mankiewicz, Nash, and Langley all worked alone, and were ignorant of each others' efforts.
Producer Arthur Freed's ideas were central to the development of the project, and shaped the resulting script. Cast members Jack Haley and Bert Lahr reportedly made contributions to the film's dialogue.
- John Fricke, Jay Scarfone, William Stillman. The Wizard of Oz: The Official 50th Anniversary Pictorial History. Warner Books, 1989.
- Aljean Harmetz. The Making of the Wizard of Oz: Movie Magic and Studio Power in the Prime of MGM — and the Miracle of Production #1060. New York, Knopf, 1977.
- Kenneth Von Gunden. Flights of Fancy: The Great Fantasy Films. Jefferson, NC, McFarland, 1989.