NCT 127 (Korean: 엔시티 127; RR: Ensiti Il-i-chil) is the first fixed and second overall sub-unit of the South Korean boy band NCT, formed and managed by SM Entertainment. They originally debuted on July 7, 2016, with their debut extended play NCT #127, with an original lineup of seven members: Taeil, Taeyong, Yuta, Jaehyun, Winwin, Mark, and Haechan. Doyoung and Johnny joined the unit in December 2016, ahead of their second EP Limitless, while Jungwoo, the final member, was introduced in September 2018 ahead of their first studio album Regular-Irregular. They are known for their experimental hip hop-based music, which they refer to as "neo music", as well as their vocal and rap abilities, choreographies, and performances.

After debuting in 2016, they broke into the domestic mainstream in 2017 with "Cherry Bomb", now recognized as one of their signature songs, and received greater international attention following the release of "Kick It" in 2020.

In April 2019, NCT 127's increasing global popularity prompted SM Entertainment to sign marketing and distribution deals with Capitol Music Group and Caroline Distribution, respectively. The unit subsequently released the EP We Are Superhuman that year and their second Korean studio album, Neo Zone, in 2020, the latter becoming their first top-five entry on the US Billboard 200 and their first release to sell over one million copies. In 2021, NCT 127 released their third Korean studio album, Sticker, and its repackaged version Favorite. With a combined 3.58 million copies sold, it broke the record for the best-selling album of all time by an act under SM Entertainment and earned the group the Daesang award at the 31st Seoul Music Awards. Sticker debuted at number three on the Billboard 200, becoming the longest and highest-charting K-pop album in the US in 2021. In 2022, NCT 127 released their fourth Korean studio album 2 Baddies, which sold 3.2 million copies and made them the second K-pop act to have three albums debut in the top five of the Billboard 200.