Earth Day, April 22, is the annual U.S. celebration of the environment and a time for Americans to assess the work still needed to protect the natural gifts of our planet. Earth Day has no central organizing force behind it, though several nongovernmental organizations work to keep track of the thousands of local events in schools and parks that mark the day. It affirms that environmental awareness is part of the country’s consciousness and that the idea of protecting the environment — once the province of a few conservationists — has moved from the extreme to the mainstream of American thought.