Sierra Club, a United States organization concerned with the preservation of the world's natural environment. The club's main concern is the protection of forests, wilderness areas, bodies of water, and other natural sites, and of wildlife. The club promotes conservation programs, publishes books and produces films about ecology, initiates legal proceedings to prevent the destruction of scenic and natural resources, and lobbies for conservation legislation. It offers numerous outdoor activities for members.

The Sierra Club was founded by the naturalist John Muir in 1892. It was influential in the establishment of the National Park Service, the U.S. Forest Service, and the National Wilderness Preservation System. It has approximately 650,000 members. Publications include a biweekly news report and a bimonthly magazine, Sierra. Headquarters are in San Francisco, California.