Effective period / Period of releases: 2016 - 2022

Members: Hyunjin, Vivi (24), Haseul, Heejin, JinSoul, Choerry, Kim Lip, Yeojin, Yves (31), Chuu (2), Go Won, 혜주

Korean name: 이달의 소녀
English name: Loona (6)

이달의 소녀 (Idarui Sonyeo = Girl of the Month), also known as Loona (6), is a South Korean girl group formed by Blockberry Creative, a subsidiary of Polaris Entertainment, set to debut in 2018. Each month, starting in October 2016 and lasting for 18 months, there is a new release of a single album or extended play, introducing a new member or sub-unit to the group.

In 2018, with the project completed, all twelve members debuted as one group.

Sub-unit:
- 이달의 소녀 1/3 – HaSeul (leader of sub-unit), ViVi, HeeJin, HyunJin
- 이달의 소녀 Odd Eye Circle – Kim Lip (leader of sub-unit), JinSoul, Choerry
- 이달의 소녀 yyxy – Yves (leader of sub-unit), Chuu, Go Won, Olivia Hye