The Sierra Club is one of the oldest and largest environmental organizations in the United States, founded in 1892 by naturalist John Muir. Its mission is to promote the conservation of the natural environment and to encourage the responsible use of the earth's resources. The organization focuses on various issues, including climate change, clean energy, and protecting public lands. Through grassroots activism, lobbying, and educational programs, the Sierra Club aims to inspire individuals to take action for a sustainable future and to preserve the beauty of nature for future generations.