XIX is the debut extended play by South Korean boy group 1the9, a project group created through the 2018 MBC survival show, Under Nineteen, composed of nine trainees from different entertainment companies that will promote for 12 months under MBK Entertainment. The album was released digitally on April 13, 2019, by MBK Entertainment.

1the9 was a South Korean boy band formed through the 2018 survival competition Under Nineteen. The group was composed of 9 members: Yoo Yong-ha, Kim Tae-woo, Lee Seung-hwan, Shin Ye-chan, Kim Jun-seo, Jeon Do-yum, Jung Jin-sung, Jeong Taek-hyeon and Park Sung-won. The group's debuting members were announced on February 9, 2019 and was initially slated to be promoting under PocketDol Studio for 12 months. After delays surrounding the COVID-19 pandemic, the group disbanded in August 2020.