21 Under 21 is an annual ranking by American music magazine Billboard beginning in 2010.
It honours young musicians under the age of 21 in the music for impact over the previous and their potential to "rule pop culture zeitgeist over the next 12 months".
Justin Bieber (2011), Lorde (2014) and Billie Eilish (2019) are the youngest acts to be #1 (all aged 17).
Willow Smith is the youngest act to appear on any ranking, (aged 9 in 2010).
Bieber; Camila Cabello; Eilish; Shawn Mendes; Lorde; Cody Simpson; Smith and Grace VanderWaal are tied for the most appearances, with five each.