The Elder Scrolls IV: Knights of the Nine is an expansion pack for the role-playing video game The Elder Scrolls IV: Oblivion. Announced on October 17, 2006, for release on November 21, 2006, the expansion was developed by Bethesda Game Studios, and published and released in North America by Bethesda Softworks; in Europe, the game was co-published with Ubisoft. The Microsoft Windows version is available either as a downloadable plug-in from the company website or as part of the retail-released Oblivion Downloadable Content Collection CD—a release that also includes all previously released official downloadable content available for Oblivion. The Xbox 360 version is available via Xbox Live Marketplace, and the PlayStation 3 version of Oblivion includes Knights of the Nine in its packaged release.

The Elder Scrolls IV: Oblivion is a 2006 action role-playing game developed by Bethesda Game Studios, and co-published by Bethesda Softworks and 2K Games. It is the fourth installment in The Elder Scrolls series, following 2002's The Elder Scrolls III: Morrowind, and was released for Microsoft Windows and Xbox 360 in 2006, followed by PlayStation 3 in 2007. Taking place within the fictional province of Cyrodiil, the game's main story focuses on the player character's efforts to thwart a fanatical cult known as the Mythic Dawn that plans to open portal gates to a demonic realm known as Oblivion.