Loona (stylized in all caps or as LOOΠΔ; Korean: 이달의 소녀; RR: Idarui Sonyeo; Japanese: 今月の少女, romanized: Kongetsu no Shōjo, lit.

The group was composed of eleven members: Heejin, Hyunjin, Haseul, Vivi, Yeojin, Kim Lip, Jinsoul, Choerry, Yves, Go Won, and HyeJu.

The group debuted as a full ensemble on August 19, 2018, with the extended play (EP) [+ +], supported by the lead single "Favorite" and the title track "Hi High".

Loona's English name is derived from the Hangul letters ㅇㄷㅇㅅㄴ, each an initial consonant in the syllabic blocks that make 이달의 소녀 (Idarui Sonyeo).

[4] Starting in October 2016 and lasting for 18 months, each member was introduced to the public through a solo promotional single as part of a pre-debut project.

[7] Loona 1/3 released the extended play Love & Live and an accompanying single of the same name on March 13, 2017,[8] with a television promotion on SBS's Inkigayo.

[11][12] Between April 2017 and July 2017, members ViVi, Kim Lip, JinSoul, and Choerry released their single albums, continuing the same Girl of the Month pattern.

[15] The group's second sub-unit, Loona Odd Eye Circle, consisting of JinSoul, Kim Lip, and Choerry, released the extended play Mix & Match and its single "Girl Front" on September 21, 2017, and began promotions on Mnet's M Countdown.

[17] On October 31, they released a repackaged edition of the extended play, titled Mix & Match, with three new songs including the single "Sweet Crazy Love".

[22] On May 30, 2018, the group's third sub-unit, Loona yyxy, consisting of Yves, Chuu, Go Won, and HyeJu, made their debut with the extended play Beauty & the Beat.

[40] Peaking at number 40, "Star" is Loona's first entry on the Billboard Mainstream Top 40, making them the second K-pop girl group to enter the chart.

[42] The following day, on June 2, a teaser was posted to Loona's official social media accounts showing twelve sets of eyes, confirming the return of member HaSeul who had been on hiatus since early 2020.

[43] On June 12, group members YeoJin, Kim Lip, Choerry, and Go Won released the song "Yum-Yum" as a collaboration with Cocomong.

[45] On June 27, 2021, Loona announced at the end of their special clip that they are making their Japanese debut on September 15 under Universal Music Japan sublabel EMI Records.

[48] Three days later, JTBC Entertainment News reported that all of the members except for ViVi and HyunJin had subsequently filed an application for a provisional injunction to suspend their exclusive contracts with Blockberry Creative.

[56] On December 12, Blockberry Creative released a teaser image announcing Loona's comeback with their sixth EP titled [0] on January 3, 2023.

[67] On June 16, it was announced that the remaining members, namely HaSeul, YeoJin, Yves, HyeJu, and Go Won, had terminated their contracts with Blockberry Creative after winning their lawsuit against the agency.

[77] On June 20, HeeJin, Kim Lip, JinSoul and Choerry won their case against Blockberry Creative over the non-existence of their exclusive contracts.