Earth Day a day dedicated to the environmental health of our planet. Earth Day is observed in the United States, Canada, and many other countries around the world with programs designed to educate people about Earth's environment and threats to the environment.  Activities intended to improve the environment also take place. Earth Day is most often celebrated on April 22, but some people observe it on March 21, the first day of spring. Activities surrounding Earth Day may continue for weeks or months.

Earth Day was first observed on April 22, 1970. The idea for a nationwide demonstration in support of Earth's environment came from Senator Gaylord Nelson of Wisconsin. Nelson is considered the founder of Earth Day. On the first Earth Day in 1970 as many as 20 million Americans in schools and communities across the country participated in rallies and demonstrations on behalf of Earth.  In New York City Mayor John Lindsay closed Fifth Avenue to automobile traffic, and thousands of people attended a fair on ecology in Central Park.

By 1990 Earth Day had become an international event, with more than 200 million people in 141 countries participating. Environmental groups use Earth Day as an occasion to draw attention to current local and global environmental problems and to discuss commonsense solutions. At fairs, festivals, and talks, people learn about air pollution, water pollution, and soil pollution; the destruction of habitats (see Ecosystem); the devastation of hundreds of thousands of plant and animal species (see Endangered Species the depletion of nonrenewable resources (see Conservation); and global warming.  They explore exhibits on such topics as conserving energy, recycling, renewing natural habitats, leading healthier lives, making their backyards friendly to wildlife, and protecting endangered species. Volunteers gather to pick up litter; clean up streams, reservoirs, and other water supplies; restore parks; plant trees; and participate in other environmental activities.