The South Korean group B1A4 was formed in 2011 in Seoul. The founder and the sponsor of the band is WM Entertainment. The lineup includes five young men, CNU, Gongchan, Baro, Sandeul, and Jinyoung. The label took a diligent approach to choosing the band members. The managers monitored the singers’ social media accounts to find worthy work samples.
The lineup was finalized on 15 April 2011. A little later, the band released a teaser of the single “O.K”. On 21st April, the group presented its first EP, Let's Fly. Two days after the album’s release, the band arranged a performance on the TV show Show! Music Core on МВС. Before April was over, the artists appeared on such shows as M! Countdown on Mnet, Music Bank on KBS, and The Music Trend on SBS.
Let's Fly appeared on the 6th spot of South Korea Gaon Album Chart. It was a big success for the debut album of a new group. The EP sold 44,000 copies. It featured such popular songs as "Remember", "Only One", "Only Learned Bad Things", and "O.K. The latter sold over 90,000 copies. At that time, many organizers tried to make a deal with WM Entertainment to book B1A4 for private events.