Pre-debut: Produce 101 and "Crush" In November 2015,
Mnet announced their new survival show that would bring together 101 trainees from 46 entertainment companies to form a unit girl group with eleven members chosen by the viewers. The show premiered on January 21, 2016, and ended on April 1, 2016. Prior to
Produce 101, some of the members of I.O.I gained recognition after appearing on other television shows:
Kim Se-jeong was a contestant on competition show
K-pop Star 2 in 2012,
Jeon So-mi was a member of the 2015 reality survival show
Sixteen, and
Choi Yoo-jung appeared in the web drama
To Be Continued. In September 2015,
Jung Chae-yeon debuted as a member of
DIA but temporarily withdrew from the group to join
Produce 101. She also had a
cameo appearance in the 2015 web drama
Sweet Temptation. It was initially planned for the group to debut on April 1, 2016, with the song "Crush," which they performed as part of the finale of the show, but YMC Entertainment and Mnet decided to postpone the debut to better prepare the group's concept and choreography with a new song as I.O.I's debut single. Its
genre was referred to as "Trapical Dutch Funk" (). On April 3, 2016, a representative gave details of the plans for the debut of the group. Instead of releasing a digital single as initially planned, I.O.I would be releasing an EP with various songs. It was also reported that the group would have their own reality show on Mnet. On the same day, the members greeted the fans for the first time as I.O.I via their official Naver
V app channel.
Debut with Chrysalis I.O.I officially debuted on May 4, 2016, through the release of their first album,
Chrysalis, accompanied with a music video for the title track "
Dream Girls". The song is a trap pop dance track co-written by
Eru and Paul with rap lyrics written by members Lim Na-young and Choi Yoo-jung. On May 5, the group held their debut stage on
Mnet's
M Countdown, performing the title track and "Knock Knock Knock". On the same day, the group held their debut showcase and fan meeting at
Jangchung Gymnasium in
Seoul.
"Whatta Man" and "Hand in Hand" On June 10, 2016, YMC Entertainment revealed Lim Na-young, Chungha, Zhou Jieqiong, Kim So-hye, Choi Yoo-jung, Kim Do-yeon and Jeon So-mi as members of I.O.I's unit group, slated to promote the group's second album during the summer of 2016. Jung Chae-yeon joined her
MBK Entertainment group
DIA for a comeback,
Kim Se-jeong and
Kang Mi-na were preparing for their debut as members of
Jellyfish Entertainment's girl group
Gugudan at the time, and
Yoo Yeon-jung was added into
Starship Entertainment's girl group
WJSN for their second comeback. On August 9, 2016, the sub-unit released a single titled "
Whatta Man (Good Man)". The song was inspired by
Linda Lyndell's "
What a Man" and was produced by
Ryan S. Jhun who also composed I.O.I's song "
Crush". The choreography for "Whatta Man" was arranged by member Chungha. On August 15, 2016, I.O.I released the digital single "Hand in Hand", a remake of the Seoul
1988 Summer Olympics theme song originally sung by
Koreana.
Miss Me? On October 17, 2016, I.O.I released their extended play titled
Miss Me?. The title track, "
Very Very Very", was written, composed and arranged by
Park Jin-young, founder of Jeon So-mi's agency
JYP Entertainment. With a rhythm of 206 bpm, the upbeat and energetic song is one of the fastest that Park has ever made. The group's special comeback show titled
I Miss You Very Very Very Much Show was aired live through Mnet on October 16, 2016, followed by the release of
Miss Me? and the title track's music video at midnight. I.O.I received their first music program trophy as a whole group with "Very Very Very" on
Show Champion on October 26.
Final activities, concert and disbandment On November 5, 2016, YMC Entertainment confirmed that I.O.I would be disbanding on January 31, 2017. The group would still be actively promoting until the end of their contracts; including guest appearance on variety shows such as
Immortal Songs: Singing the Legend,
Yang and Nam Show and
Knowing Bros. From January 20 to 22, 2017, I.O.I held their final concert titled
Time Slip – I.O.I. The three-day concert was held in Jangchung Gymnasium, where the group held their debut showcase. On January 10, 2017, it was revealed that I.O.I had received songs from various producers and songwriters as potential songs for their final release, including
B1A4's
Jinyoung. On January 17, YMC Entertainment announced that the group's final track before official disbandment would be "
Downpour", written and co-produced by
Seventeen's Woozi. The ballad was personally chosen and recorded by all eleven members of the group. The digital single and its music video was released the next day at midnight. I.O.I's last schedule as a group was on January 25, 2017. They filmed a new
CF for school uniform brand Elite along with boy group
Pentagon. The band officially disbanded on January 29, with the members' last television show appearance on
MBC's Section TV and the fan cafe closing down on the 31st. It was also announced on January 31 that I.O.I's song "Downpour" won
Inkigayo's final January 2017 trophy with no live broadcast due to Lunar New Year's Day.
Subsequent reunions On July 1, 2019, Studio Blu confirmed that the group would return in October 2019 with nine members, excluding Yoo Yeon-jung and Jeon So-mi. On September 6, the planned comeback was postponed to December. On October 29, the comeback was canceled due to scheduling conflicts between the members and the ongoing
Mnet vote manipulation investigation. On May 4, 2021, the 5th anniversary of the group's debut, the group held a reunion livestream.
Mina was absent from the stream, while
Jieqiong joined via video call. On February 23, 2026,
Swing Entertainment announced that the group will reunite for a new album release in May, without Mina and Jieqiong. Swing also confirmed that they will manage the group's promotional activities for the album and their 10th anniversary. On April 21, Swing Entertainment announced that I.O.I's third extended play
I.O.I : Loop would be released on May 19. The pre-release single "Goodbye with a Smile", produced by singer-songwriter
Jinyoung and recorded in 2016, was released on May 4. ==Members==