Kep1er (/ˈkɛplər/; Korean: 케플러; RR: Kepeulleo; Japanese: ケプラー, Hepburn: Kepurā) is a South Korean girl group formed by CJ ENM through the Mnet reality competition show Girls Planet 999 in 2021. The group consists of seven members: Kim Chae-hyun, Huening Bahiyyih, Choi Yu-jin, Kim Da-yeon, Seo Young-eun, Ezaki Hikaru, and Shen Xiaoting. Originally a nine-piece ensemble, former members Kang Ye-seo and Sakamoto Mashiro departed from the group in July 2024.

The group debuted on January 3, 2022, under the co-management of WakeOne and Swing Entertainment with their first extended play (EP) First Impact. Upon its release, the group received immediate commercial success, selling approximately 400,000 copies and peaking at number 1 on South Korea's Gaon Album Chart. In addition, both the EP and its lead single "Wa Da Da" charted on the Billboard Global 200 and World Digital Songs respectively. The early success subsequently hailed them as the New Wave of the Year at several awards ceremonies, including Asia Artist Awards and Seoul Music Awards.

The group's Japanese debut single, "Fly-Up", was released on September 7, 2022, under the Sony Music Entertainment Japan subsidiary Ariola Japan. Debuting at number two on Oricon Singles Chart and with over 100,000 unit sales, the single was certified gold by the Recording Industry Association of Japan (RIAJ).

Since September 30, 2024, as part of the label reorganization of Swing Entertainment, Klap Entertainment will be co-managing the group alongside WakeOne.