The Greater Yellowstone Ecosystem is one of the last remaining large, nearly intact ecosystems in the northern temperate zone of the Earth.^[1] It is partly in Yellowstone National Park.

The Greater Yellow Ecosystem (GYE) is a kind of natural laboratory in landscape ecology and geology. It is a world-renowned recreational site, and home to the animals of Yellowstone.

The Yellowstone National Park boundaries were drawn in 1872 to include all the geothermal basins in the area. By the 1970s, the grizzly bear's (Ursus arctos) range in and near the park became the unofficial minimum boundary of a Greater Yellowstone ecosystem. This had at least 16,000 square kilometres (4,000,000 acres). Since then, definitions of the greater ecosystem's size have steadily grown larger. A 1994 study listed the size as 76,890 square kilometres (19,000,000 acres), while a 1994 speech by a Greater Yellowstone Coalition leader enlarged that to 80,000 square kilometres (20,000,000 acres).

In 1985 the United States House of Representatives Subcommittees on Public Lands and National Parks and Recreation held a joint subcommittee hearing on Greater Yellowstone. The result was a 1986 report by the Congressional Research Service which said that different agencies were not working well together, and the area's essential values were at risk.

There are other areas within the Greater Yellowstone area which are managed by federal authorities. They include the Gallatin, Custer, Caribou-Targhee, Bridger-Teton and Shoshone National Forests, the John D. Rockefeller, Jr. Memorial Parkway, the National Elk Refuge and Grand Teton National Park. The GYE also includes some private lands around those managed by the U.S. Government.

Outside of Yellowstone National Park, ten wilderness areas have been established in the National Forests since 1966 to get more habitat protection than usual.