Yungbok is a uniform worn by public officials of the Joseon Dynasty when they were accompanying the king, dispatched to a foreign country as an envoy, or in a time of national emergency. It consists of a cheollik coat with pleats and a julip hat. Wearing this uniform had been forbidden in ordinary times, yet became permitted after the Japanese invasion of 1592. Yungbok is comprised of a hat, a coat, a waist cord, and leather boots, while different colors were employed for the hat and coat in order to distinguish the wearer’s status. Third- or higher rank officials wore a purple hat and a navy coat, while officials lower than third rank wore a black hat and a cerulean coat. The hat was decorated with a heron-shaped jade ornament and a feather-like ornament. The coat has a straight collar with its lower part connected with the upper part at the waist. Its name was written as 帖裏, 貼裏, 帖裡 (chomni), 天益, 天翼, 千翼 (cheonik), and 綴翼, 膝翼 (cheolik) in Chinese, and cheollik, tyeollik, chyeomni, and chyeonnik in Korean. The cheollik coat began to be worn in the mid-Goryeo Dynasty, whiles its use became varied among different social classes in the early Joseon Dynasty, and became commonplace in the mid-Joseon Dynasty. Throughout different eras, the coat underwent changes with regard to the ratio of the upper and lower parts, pleats patterns, and shapes of the collar and sleeves. The upper and lower parts were almost identical in length in the early Joseon Dynasty, yet the lower part became gradually longer to more than twice the length of the upper part in the late Joseon era. At the same time, sleeves turned from narrow ones to rounded ones. The pleats of the lower part were mostly thin in early Joseon, but wider pleats became more prevalent in late Joseon.