Gugudan (Hangul: 구구단, stylized as gugudan or gu9udan) is a South Korean girl group formed in 2016 by Jellyfish Entertainment. The group consists of nine members: Mimi, Hana, Haebin, Nayoung, Sejeong, Sally, Soyee, Mina and Hyeyeon.

Pre-debutIn January 2016, Kim Na-young, Kim Se-jeong and Kang Mi-na were introduced as Jellyfish Entertainment's first female trainees on the Mnet survival show Produce 101 where 101 female trainees from various companies competed to debut in an 11-member girl group that would promote for a year under YMC Entertainment.After placing 2nd and 9th respectively in the final episode, Sejeong and Mina eventually debuted as members of I.O.I in May 2016.2016-present: Debut with "Wonderland"Despite denying earlier reports about Sejeong and Mina debuting in a 7-member girl group in June, the company confirmed on June 7 that the two I.O.I members would debut within the month in what would be the company's first girl group. Because of YMC Entertainment's special terms in which I.O.I's members are allowed to do activities under their respective companies while IOI was on break or while the group promoted in sub-units, there were no complications with the plan.Nayoung was also confirmed as a member on June 10[6] and on June 13, the company revealed that Gugudan would be a 9-member group. On June 17, Jellyfish Entertainment announced the group name.On June 22, the group confirmed that they were going for a "mermaid" concept. Following the announcement, a highlight medley of the group's debut mini-album was released on June 24 and they eventually debuted on June 28, 2016 with the mini-album, Act. 1 The Little Mermaid, with "Wonderland" as the title song. The song's music video was released online via a live countdown on the Naver V App.