Doom 3 (stylized as DOOM³) is a 2004 horror first-person shooter video game developed by id Software and published by Activision.

Doom 3 is set on Mars in 2145, where a military-industrial conglomerate has set up a scientific research facility into fields such as teleportation, biological research, and advanced weapons design. The teleportation experiments open a gateway to Hell, resulting in a catastrophic invasion of the Mars base by demons. The player controls a space marine who fights through the base to stop the demons attacking Mars and reaching Earth.

Doom 3 is the first reboot of the Doom series, ignoring the events of the previous Doom games but is stated in Doom RPG as a prequel to the first game. Doom 3 utilizes the id Tech 4 game engine, which has since been licensed out to other developers, and later released under the GNU General Public License in November 2011.