The creator of Squid Game, Hwang Dong-hyuk, developed the show in 2009. However, it was rejected by media companies and actors for 10 years. Ironically, after Netflix picked it up and the show became a massive success, Hwang rejected Netflix' request for more episodes several times because he had only ever intended to make one season. However, making season 1 had given him some new ideas, so he agreed to make two more seasons; anything beyond that would be without his participation. At the end of season 3, writing and directing every episode himself as well as the show's dark subject matter had exhausted him so much that he half-jokingly said that he would retire to a uninhabited island, where Netflix could no longer bother him.
Chae Kyoung-sun, the set designer, felt this was her most challenging project as not only did she have to create something child-like and whimsical, but also creepy and menacing in addition to the safety concerns for the actors.
The phone number used in the series was a real phone number. However, the only difference is that it has eight digits in the series, while real numbers in South Korea always have ten. When the callers dialed that number, their phones automatically added the prefix "010", which turned it into a real number. As a result, the owner of it was called more than 4,000 times a day. Netflix later announced that the number will be altered.
The worker jumpsuits were chosen for their loose design to mask the gender of the workers and to create a colony vibe to the setting. The soldiers' masks were designed specifically to resemble the face of an ant.
The scenes featuring Sae-byeok and Ji-yeong were written to show the two most innocent characters out of the other players as they were the youngest and had used their extremely limited time to create a close bond. It is a juxtaposition to Gi-hun and Sang-woo, who were childhood friends but had become increasingly distanced through the games.