The group's leader, Taeyeon, was cast in 2004 after winning first place in the S.M. Youth Singing Competition. That same year, member Tiffany auditioned at S.M.'s Starlight Casting System in Los Angeles, and joined the company in October 2004. The final member of the group to be added was Sunny, who had become an S.M. trainee in 1998 and trained for five years before moving to another company, Starworld. At Starworld, she trained to debut in a duo named Sugar, which never debuted. In 2007, on the recommendation of Korean-Japanese singer IconiQ, Sunny moved back to S.M. Entertainment and became a member of Girls' Generation.