I.O.I (Hangul: 아이오아이; also known as IOI or Ideal of Idol) was a South Korean girl group formed by CJ E&M through the 2016 reality show Produce 101 on Mnet. The group was composed of eleven members chosen from a pool of 101 trainees from various entertainment companies: Lim Na-young, Kim Chung-ha, Kim Se-jeong, Jung Chae-yeon, Zhou Jieqiong, Kim So-hye, Yoo Yeon-jung, Choi Yoo-jung, Kang Mi-na, Kim Do-yeon and Jeon So-mi. They debuted on May 4, 2016 with the EP Chrysalis and actively promoted as a whole and as a sub-unit for less than a year. The group's concert titled Time Slip – I.O.I, which was held on January 20 to 22, 2017, marked their last group activity on stage. They officially disbanded at the end of January 2017 and returned to their respective agencies.

Pre-debut: Produce 101 and "Crush"

Main article: Produce 101

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. 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 11 members chosen by the viewers. The show premiered on January 21, 2016 and ended on April 1, 2016.

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. 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.[16] 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. On April 4, 2016, Mnet released the music video teaser for I.O.I's pre-debut track "Crush". The next day, the song was released as a digital single, followed by its music video. Its genre was referred to as "Trapical Dutch Funk" (Hangul: 트래피컬 더치 펑크).

Debut with Chrysalis

On April 11, 2016, it was announced that I.O.I would debut with an EP on May 4, 2016, and would hold a debut showcase and fan meeting the following day at Jangchung Gymnasium. LOEN Entertainment would assume the distribution duties for I.O.I's releases starting from their debut EP. On April 27, YMC Entertainment announced that I.O.I's first album was titled Chrysalis. Five days later, the music video teaser was released. I.O.I officially debuted on May 4, 2016 through the release of their first album and music video for title track "Dream Girls". The song is a trap pop dance track co-written by singer-songwriter-producer Eru (who used the pen name Famousbro) and composer 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 May 11, Jung Chae-yeon of MBK Entertainment re-joined DIA for the group's comeback in June. On May 27, it was revealed that I.O.I would start promotions with sub-units and solo debuts of members in summer of 2016, and would likely disband at the end of January 2017. On June 7, it was announced that Kim Se-jeong and Kang Mi-na of Jellyfish Entertainment had returned to their agency to prepare for their official debut as members of the girl group Gugudan at the end of June.

I.O.I on July 16, 2016

On June 10, 2016, YMC Entertainment revealed Lim Na-young, Kim Chung-ha, 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. On July 29, 2016, it was announced that I.O.I would be dropping their new single on August 9. The unit group finished filming their music video on July 20 and began preparations for the single's release and promotions. On August 2, 2016, a group image teaser was released through I.O.I's SNS with a caption "WXAXTX X XAN". Two days later, YMC Entertainment revealed the music video teaser for the group's new single "Whatta Man (Good Man)". The song was inspired by Linda Lyndell's "What a Man", with a 1993 version released by Salt-n-Pepa with En Vogue, 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 Kim Chung-ha. It was revealed that three teams were contacted to make the choreography for the song but Chung-ha's was chosen because it was deemed to be the highest quality. 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 August 30, 2016, YMC Entertainment announced that I.O.I was preparing for a comeback with the eleven members in October, though the exact date had not yet been set. On September 22, the agency confirmed that I.O.I had begun recording for the new album as a full group, with the title track being produced by Park Jin-young, founder of Jeon So-mi's agency JYP Entertainment, who had produced several girl group hit songs including Wonder Girls' "Tell Me" and "Nobody" and miss A's "Bad Girl Good Girl". It was revealed that Park would oversee the group's choreography, outfits, music video and photo shoot.] It was also reported that the new EP would be their last album before disbanding at the end of the year. The members would return to their respective agencies afterwards.

On September 28, 2016, it was confirmed that I.O.I's new album was set to be released on October 17, 2016. On October 11 at midnight, I.O.I announced the new extended play titled Miss Me?, followed by four image teasers of the members over the next two days. Three days later, the music video teaser for the title track personally written, composed and arranged by Park Jin-young titled "Very Very Very" (너무너무너무) was released. 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 at 23:30 KST, followed by the release of Miss Me? and the title track's music video at midnight. I.O.I held the showcase for their second EP at Yes24 Live Hall located in Seoul on October 17. During the event, it was revealed that the group is planning to hold their final concert on January 20 to 22, 2017, though the details were still undecided. When the press asked about a possible reunion after disbandment, the members said they would want to reunite after five years. I.O.I received their first music program trophy as a whole group with "Very Very Very" on the October 26th episode of Show Champion.

Last activities, final 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. On November 27, I.O.I announced their final solo concert titled Time Slip – I.O.I from January 20 to 22, 2017. The three-day concert was held in Jangchung Gymnasium, where the group held their debut showcase.

I.O.I's unit group in December 2016

On December 21 2016, it was reported that I.O.I's unit group would be releasing a digital single in January 2017 with no promotions on music shows. 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 11 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.

Post-disbandment

The eleven members of I.O.I returned to their respective agencies after disbandment. Jung Chae-yeon, Kim Se-jeong, Kang Mi-na and Yu Yeon-jung re-joined their existing and permanent groups, DIA, Gugudan, and Cosmic Girls, respectively. Kim So-hye joined SBS Power FM Bae Sung-jae's Ten Radio as a fixed member. She debuted as an actress with a music video and web drama in the first half of 2017. Kim Chung-ha opened her official fancafe ahead of her solo debut under M&H Entertainment. She officially debuted as a soloist on June 7, 2017 with the release of her first extended play, Hands on Me. Lim Na-young and Zhou Jieqiong (or Kyulkyung) debuted with Pristin on March 21, 2017. Choi Yoo-jung and Kim Do-yeon debuted with Weki Meki on August 8, 2017.

Jeon So-mi signed a formal contract with JYP Entertainment to start solo activities such as variety shows. She joined the cast of Sister's Slam Dunk Season 2 which premiered on February 10, 2017. In November 2017, Lim Na-young, Kim Chung-ha, Zhou Jieqiong, Choi Yoo-jung and Kim Do-yeon had a collaboration performance with AKB48 at the 2017 Mnet Asian Music Awards in Japan.- Wikipedia