Coming of Age Day (成人の日, Seijin no Hi^?) is a Japanese holiday held annually on the second Monday of January. It is held in order to congratulate and encourage all those who have reached the age of majority (20 years old (二十歳, hatachi^?)) over the past year, and to help them realize that they have become adults. Festivities include coming of age ceremonies (成人式, seijin-shiki^?) held at local and prefectural offices, as well as after-parties amongst family and friends.

Coming of age ceremonies have been celebrated in Japan since at least 714 AD, when a young prince donned new robes and a hairstyle to mark his passage into adulthood.^[1] The holiday was first established in 1948, to be held every year on January 15.^[2] In 2000, as a result of the Happy Monday System, Coming of Age Day was changed to the second Monday in January.^[3]