SD-6 is a fictional organization featured in the television series Alias. It operates as a covert branch of the CIA, involved in various illegal activities and espionage. The organization is known for its secretive nature and manipulation of information to achieve its goals. In the series, the protagonist, Sydney Bristow, discovers that SD-6 is not a legitimate government agency but rather a front for a criminal syndicate. This revelation drives her to work as a double agent, aiming to dismantle SD-6 while still fulfilling her duties to the CIA.