By2 is a Singaporean duo based in China. The duo is composed of twin sisters Miko Bai and Yumi Bai.
By2 gained attention at the start of their career with their first two studio albums, but it was not until 2010 when they released their third studio album, Grown Up, for which gained them significant popularity, with the album topping Taiwan's music chart, "G-Music" and several music charts in China. The album was responsible for 33 percent sales of albums in the Chinese market and 18 percent sales of albums in Taiwan during the week of 9 to 15 April 2010.