Mountain Day refers to three different and unrelated events: (1) Mountain Day, a student celebration in some colleges in the United States in which classes are cancelled without prior notice, and the student body heads to the mountains or a park, (2) International Mountain Day, held each year on 11 December, which was established by the UN General Assembly in 2003 to encourage sustainable development in mountains, and (3) Mountain Day, a national holiday in Japan as of 2016.