Wonder Girls was a South Korean girl group formed by JYP Entertainment. The group debuted in February 2007 with the single "Irony" and 5 members: Yeeun, Sunye, Sunmi, Hyuna and Sohee. After Hyuna's departure in July, Yubin was added into the group prior to the release of their debut studio album, The Wonder Years. The album spawned the hit single "Tell Me", which topped various South Korean music charts.
Wonder Girls further established themselves as one of the top girl groups in the country with the hit singles "So Hot" and "Nobody", released in 2008. After being released as a single in the U.S. in 2009, "Nobody" charted at No. 76 on the Billboard Hot 100, making Wonder Girls the first South Korean act to enter the chart. The group began their entry into the American market the same year as an opening act for the Jonas Brothers' World Tour, performing English versions of their songs.
In early 2010, Sunmi left the group to pursue an academic career and was replaced by Hyerim prior to the worldwide release of the single "2 Different Tears" later that year. Their second studio album, Wonder World, yielded the hit single "Be My Baby".