Bethesda stated it would be working on Fallout 3 in July 2004, but principal development did not begin until after The Elder Scrolls IV: Oblivion was completed. Bethesda announced their intention to make Fallout 3 similar to the previous two games, focusing on non-linear game play, a good story, and true "Fallout humor." Bethesda also stated the game is targeted for a rating of M for Mature, and would have the same sort of adult themes and violence that are characteristic of the Fallout series. Fallout 3 uses a version of the same Gamebryo engine as Oblivion, and was developed by the same team. Initially Bethesda held the right to make only 3 Fallout games with royalties to be paid to Interplay.
In 2006, Bethesda bought the full Fallout franchise leaving Interplay the right to make Fallout Online. Between May 2 and June 5, 2007 Bethesda showcased 5 pieces of concept art by Craig Mullins on the Fallout 3 website during the countdown to the teaser. The cinematic teaser trailer for Fallout 3, consisting of the first part of the intro, was released by Bethesda Softworks on June 5, 2007, after a 30 day countdown on the Fallout 3 website. On August 2, 2007, the game's website was opened.