Season 1 begins and ends the same: "Sometimes it seems like it happened to someone else, like maybe it was a story I heard. Even though I know it happened." Max says it atop the Space Needle in the Pilot and Logan says it atop the Space Needle in the season finale.
When the character of Alec was conceived for the series' season 2, the writers knew they wanted him to be a somewhat amoral X5 with a sharp wit. They chose to immediately hire Jensen Ackles for the role, who had previously played a rogue serial killing X5 in a season 1 episode. They explained the actor's return in a different role by saying that Alec was his former, and deceased, character's twin. Although they had only seen Ackles as a dramatic actor in his previous roles, everyone in the production was pleased to see that Ackles had a natural talent as a comedian.
Several scenes of the children training at Manticore were edited for the opening scenes of Hitman (2007), which has a similar theme of genetically enhanced children being trained as assassins and a protagonist (Agent 47) with a barcode on the back of his neck.
Although both shows are listed as only having 21 episodes, they each have 22 episodes when re-aired. The first season has 21, but the pilot is approximately eighty-five minutes (twice the length of other episodes). The second season (and series) finale, "Freak Nation," is an hour and a half, which splits the episode during re-airings.
Max's Phone number, clearly heard near the beginning of the episode "Harbor Lights" when dialed by Logan, (He is forwarded to her pager) are the first few (9) notes of the theme song to "The Wheel of Fortune".
Co-producer Kenneth Biller said in a Season 2 DVD interview that their filming location, Vancouver, would not allow them to "trash" a nice neighborhood. Hence, Terminal City had to be built from scratch.