Earth Day is an annual event, celebrated on April 22. Events are conducted worldwide to demonstrate support for environmental protection. It was first celebrated in 1970, and is now coordinated globally by the Earth Day Network and celebrated in about 192 countries each year.

Earth Day was founded by United States Senator Gaylord Nelson as an "environmental teach–in" first held on April 22, 1970. Nelson chose the date hoping to maximize participation in college campuses. The week of April 19–25 was ideal as it did not fall during exams or spring breaks and was late enough in spring to have a decent weather. The Earth day network, an organization launched by Denis Hayes, took the event international in 1990 and organized events in 141 nations.