Earth Day is a day early each year on which events are held worldwide to increase awareness and appreciation of the Earth's natural environment. Earth Day is now coordinated globally by the Earth Day Network,^[1] and is celebrated in more than 175 countries every year.^[2] In 2009, the United Nations designated April 22 International Mother Earth Day.^[3] Earth Day is planned for April 22 in all years at least through 2015.^[4]

The name and concept of Earth Day was allegedly pioneered by John McConnell in 1969 at a UNESCO Conference in San Francisco. The first Proclamation of Earth Day was by San Francisco, the City of Saint Francis, patron saint of ecology. Earth Day was first observed in San Francisco and other cities on March 21, 1970, the first day of spring in the northern hemisphere. This day of nature's equipoise was later sanctioned in a Proclamation signed by Secretary General U Thant at the United Nations where it is observed each year. About the same time a separate Earth Day was founded by United States Senator Gaylord Nelson as an environmental teach-in first held on April 22, 1970. While this April 22 Earth Day was focused on the United States, an organization launched by Denis Hayes, who was the original national coordinator in 1970, took it international in 1990 and organized events in 141 nations.^[5][6] Numerous communities celebrate Earth Week, an entire week of activities focused on environmental issues.