Girl's Day (걸스데이) is a five-member South Korean girl group under the management of Dream Tea Entertainment. The five members are: So Jin, Ji Hae, Min Ah, Yura & Hyeri. The fan's name is "Daisy" or "Dai5y".

DreamTea Entertainment started Girl's Day promotions before their debut with the creation of an official Cafe, YouTube channel, and Twitter accounts for the group and each member. A forum made by fans was also recognized by the company as their official international forum. The group also released dance flash mobs before their debut on the commercial and entertainment districts of Seoul gaining much interest.

On July 7, the group released their first MV, "Tilt My Head", and two days later their debut mini-album "Girl's Day Party 1".

Only two months after their debut, on September 12, it was announced through the group's official Twitter that members Ji Sun and Ji In left the group and two new members would be added to the group: "Two of our precious members of Girl's Day are to be replaced. They are Ji Sun and Ji In. Ji Sun will study music more to find her own character in music, as she wanted. And Ji In is attracted in acting so she will concentrate on acting career." Two days later, on September 14, the two new members were announced, Yura and Hyeri. On October 29, the new line-up released the group's first digital single, "Girl's Day Party 2". On October 30 the MV for their lead track, "Nothing Lasts Forever" was released.