The third season of the military science fiction television series Stargate SG-1 commenced airing on Showtime in the United States on June 25, 1999, concluded on Sky1 in the United Kingdom on March 8, 2000, and contained 22 episodes. The third continues the plot started in season one, the third season follows SG-1 in their fight against the Goa'uld Empire's System Lords, the main being Sokar until "The Devil You Know" and then Apophis after regaining power after the event in "The Devil You Know." The season introduces the long unseen and unnamed enemy of the Asgards, the Replicators who are self-replicating machines that seek to convert all civilizations into more of themselves, thus posing a dire threat to all other beings. The Replicators are first mentioned, but not named, in season three episode "Fair Game".
The one-hour premiere "Into the Fire", which debuted on June 25, 1999 on Showtime did not receive any syndication rating, but overall got a high viewership level. The series was developed by Brad Wright and Jonathan Glassner, who also served as executive producers. Season 3 regular cast members include Richard Dean Anderson, Michael Shanks, Amanda Tapping, Christopher Judge, and Don S. Davis.