Tom Clancy's Splinter Cell: Chaos Theory is a stealth game developed by Ubisoft Montreal and Ubisoft Milan. The game was released for GameCube, PlayStation 2, Windows and Xbox in March 2005. Handheld versions for the Nintendo DS, mobile, and N-Gage were also released.

Splinter Cell: Chaos Theory is the sequel to Splinter Cell: Pandora Tomorrow and the third game in the Splinter Cell series endorsed by novelist Tom Clancy. As with previous entries in the franchise, Chaos Theory follows the activities of Sam Fisher, an agent working for a covert-ops branch within the NSA called "Third Echelon". The game has a significantly darker tone than its predecessors, featuring more combat and the option for Fisher to kill people he interrogates instead of merely knocking them out. As a result, it was the first Splinter Cell game to receive an M-rating by the ESRB, an assessment which has since been applied to all subsequent releases in the series. Actor Michael Ironside reprised his role as Fisher. Don Jordan returned from the original game to voice Third Echelon director Irving Lambert, and Claudia Besso returned as the hacker and analyst Anna Grímsdóttir, having both been replaced by Dennis Haysbert and Adriana Anderson, respectively, in Pandora Tomorrow.

Chaos Theory's Xbox and PC versions of the game received critical acclaim; the GameCube and PlayStation 2 iterations were also released to generally positive reviews. Chaos Theory was a commercial success, selling 2.5 million units across all platforms within a month of its release. Official Xbox Magazine named it the Xbox "Game of the Year" (2005) for its strong gameplay and lifelike graphics, and it received the highest-ever review score for the magazine at the time. It is considered one of the greatest video games ever made. A remastered HD edition was bundled with the first two games of the series as part of the Splinter Cell Trilogy for the PlayStation 3, released on December 20, 2010. Another port titled Tom Clancy's Splinter Cell 3D was released for the Nintendo 3DS on March 25, 2011. A sequel, titled Double Agent, released in 2006.