The Sierra Club is one of the oldest and largest environmental organizations in the United States, founded in 1892 by naturalist John Muir. Its primary mission is to promote the conservation of the natural environment through grassroots activism, education, and lobbying efforts. The organization focuses on various issues, including climate change, clean energy, and protecting public lands. With over 3.8 million members, the Sierra Club engages in numerous campaigns and initiatives aimed at preserving ecosystems and promoting sustainable practices. The organization also organizes outdoor activities, such as hiking and camping, to encourage people to connect with nature and foster a sense of environmental stewardship.