Willis O'Brien's Gwangi was an epic movie that was never completed. The visual effects genius that brought King Kong to life made elaborate plans for a spectacular motion picture project. Gwangi combined elements of The Lost World and King Kong with cowboys, rodeos, and Western themes. Like all of O'Brien's projects, it was meticulously pre-planned. Numerous artists were employed to illustrate the action and visual effects scenes. Particular scrutiny was placed on how each scene would be brought to the screen. The technical supplement was a unique document prepared by Willis O'Brien to augment the script and storyboards for Gwangi. It details all of the various elements - live-action, animation, background plates, process screens, miniatures, optical printing, and mechanical effects - required to produce the intricate visual imagery that O'Brien was famous for. The technical supplement is presented here in its original form.