The song experienced commercial success in South Korea, peaking at number one for two consecutive weeks on both the Gaon Digital Chart and K-pop Hot 100. It underperformed in Japan, however, peaking at number 110 on the Oricon Singles Chart.
"U&I" was released digitally via YMC Entertainment on July 12, 2013, in conjunction with Ailee's second extended play A's Doll House, serving as its lead single. In Japan, "U&I" was released as the singer's second Japanese single via Warner Music Japan on March 19, 2014. It was physically distributed in multiple versions: a regular edition CD single, a special edition CD, and a limited edition CD + DVD bundle.
Prior to the single's release in the country, "U&I" was selected as the official theme song for several fashion events, including 2014 S/S 'Kobe Collection' and 'Tokyo Girls Collection'.[1]
