[+ +] (read as "plus plus") is the debut extended play (EP) by South Korean girl group Loona.

The EP was the second highest selling debut album by a girl group in 2018 with 52,823 physical copies sold.

[2][3][4][5] Then, between April and July 2017, members ViVi, Kim Lip, JinSoul and Choerry were officially introduced.

[6][7][8][9] Finally, between November 2017 and March 2018, members Yves, Chuu, Go Won and HyeJu (formerly Olivia Hye) were officially introduced.

[13] Blockberry Creative released a 26-second teaser titled "X X" on October 14, 2018, on Loona's official YouTube channel, which featured events from the "Hi High" music video in reverse.

[19] The album opens with a dreamy instrumental intro titled "+ +" that features smooth synthesizers, artificial summery guitar licks, digital finger snappings, the continuous change of the melodies and the layering of whispered vocals and manipulated whistle samples.

[25] [X X] debuted at number 4 on the US World Albums Chart with 2,000 downloads sold and 721,000 on-demand audio streams for its songs.