During his QuakeCon keynote, Id Software co-founder and lead programmer John Carmack announced that the full source code of Doom 3 will be released shortly after the launch of the studio's next game: Rage.
Doom 3 was released in 2004 and it runs on id Tech 4 graphics engine and Rage runs on its successor id Tech 5 graphics engine. Rage is scheduled for release in October this year.
Carmack confirmed that his studio's parent company, Zenimax, has approved the source code release. The famous developer then urged other developers to release the source code of their old games for the good of the whole development community.