"Good Day" (Korean: 좋은 날; RR: joheun nal) is a song recorded in two languages (Korean and Japanese) by South Korean singer IU. The Korean version was released on December 9, 2010, as the lead single for IU's third extended play (EP) Real. It was written by Kim Eana, while production was handled by Lee Min-soo. The Japanese version was originally included on IU's first Japanese extended play I□U, released on December 14, 2011, before being released on March 21, 2012, as IU's first single album Good Day.