NCT 127 (Korean: 엔시티 127; RR: ensiti il-i-chil; stylized in all caps) is the second sub-unit of the South Korean boy band NCT, formed and currently managed by SM Entertainment. Their unit name is a combination of the acronym for Neo Culture Technology which is the meaning for their parental group's unlimited members, and as the unit is localized in Seoul, hence the number "127" representing the longitude coordinate of the city. Originally debuted on July 1, 2016, the unit's original line up was composed of seven members: Taeil, Taeyong (leader), Yuta, Jaehyun, Winwin, Mark, and Haechan for their debut extended play NCT #127, which was a commercial success upon its release and earned the unit several nominations, eventually won them the Best New Group title at several South Korea music awards in 2016. Member Doyoung and Johnny then joined the unit in December 2016, ahead of their next extended play Limitless in 2017. Jungwoo was then introduced as the tenth and latest member to the unit in September 2018, followed by the group's first studio album Regular-Irregular later in October 2018. The ten-member unit is NCT's first fixed sub-unit, followed by the debut of Chinese-based unit WayV in early 2019.

Following the unit's debut in July 2016 with their self-titled extended play, NCT 127 has since released two full-length studio albums, two repackage releases and four extended plays for their promotion activities in South Korea. They eventually achieved breakthrough recognition in 2017 with "Cherry Bomb", hailed as one of the group's signature song and musical identity, further explored international breakthrough success with the release of their first studio album and its lead single "Regular" in 2018. The unit also ventured into the Japanese music scene with a Japanese version of their second single "Limitless", has released an extended play and a full-length studio album as of 2019. NCT 127 then continued to expand their promotion globally, having signed with Capitol Music Group and Caroline Distribution for a worldwide marketing and distribution deal with the group's native label SM Entertainment in April 2019, followed by the release of We Are Superhuman and their second full-length Korean album Neo Zone, with the latter becoming their first top-five entry on the US Billboard 200 chart, and subsequently the unit's first release to sell over a million copies as of May 2020.