The written precursors to screenplays were called "scenarios" and were simple documents written for short silent films. Screenwriters were called "scenarists," and their scripts, mere descriptions of action with little dialog, only vaguely resembled the screenplays of today. Before 1919 many scenarios were simply committed to memory and never even got as far as ink and paper.
With the success of epic films made by directors such as silent film legend D.W. Griffith, the major studios implemented story departments. Screenwriters were contracted and put on salaries, and produced screenplays in a mass production system in rooms filled with typewriters.
John Howard Lawson published the first essential guide to writing a screenplay in 1949. The fundamental rules for formatting a script for film can be traced to his "Theory and Technique of Playwriting and Screenwriting."
While the writing process and format of the movie script did not change greatly for decades after Lawson's time, in the past several years it has changed dramatically with the addition of novel software platforms. New programs allow the script to be integrated with other aspects of production, from casting, prop management, story-boarding and even post-production.
A majority of scenarists and the first generation of screenwriters were women. Frances Marion was the highest paid screenwriter in the United States until the mid-1930s, and served as the Vice President of the Writer's Guild of America for years.