Creator J. J. Abrams said he got the idea for the show while working in the Felicity writers room, wondering 'Wouldn't it be really cool if Felicity were recruited by the C.I.A.?'

Abrams told the New York Times that Alias was never meant to be a realistic portrayal of how the CIA operates, saying he was more interested in what worked for the story than in doing 'a documentary on Langley procedure.'

The series premiered the same month as the September 11 attacks.

A shocking retcon involving a document authorizing Jack Bristow to execute Irina in Season 4 was apparently created to cover for actress Lena Olin not returning to the series.

Jennifer Garner's real-life pregnancy was written into the plot in Season 5, with her character Sydney Bristow also becoming pregnant.

ABC gave the show a four-month hiatus to allow Jennifer Garner to give birth to her first child before returning with new episodes in April 2006.

The show featured numerous famous guest stars in small or single-episode roles, including Quentin Tarantino, Faye Dunaway, Roger Moore, Ethan Hawke, Ricky Gervais, David Carradine, Rutger Hauer, and David Cronenberg.

Filming primarily took place in the greater Los Angeles area, with studio shooting at Walt Disney Studios in Burbank; the U.S. Bank Tower stood in for CIA headquarters, and only one episode was ever filmed outside the Los Angeles region, at the Aladdin Casino and Resort in Las Vegas.

The season one soundtrack's 26 tracks were all composed by Michael Giacchino, except for the opening theme, which was composed by series creator J. J. Abrams himself.

The Alias cast filmed at least two comedic spoofs of the show, including a 2002 Monday Night Football skit where Sydney infiltrates the Washington Redskins locker room, and a 2003 ABC 50th anniversary special skit featuring Peter Falk as Columbo joining the CIA team.

In August 2003, the real CIA enlisted Jennifer Garner to appear in an actual recruitment video shown at career fairs and college campuses, with a CIA officer noting that Garner and her character Sydney Bristow reflected qualities the agency looks for in new officers.

The Super Bowl XXXVII lead-out episode 'Phase One' drew a series-high 17.4 million viewers but retained only 19 percent of the Super Bowl audience, partly due to an unusually long 40-minute post-game show that pushed its start past 11:00 p.m. ET, giving it the lowest post-Super Bowl ratings in the 18-49 demographic until Elementary in 2013.