Wolves once ranged over most of the United States but were eliminated from the northern Rockies by the 1930s. From 1918 to 1935, government bounty hunters shot and killed predators including coyotes, wolves, and mountain lions. By 1926, the last wolf was eliminated from Yellowstone National Park. This was the result of an aggressive government-sponsored predator control program and public policy that was based on the assumption that wolves had no value.

In 1987 a Rocky Mountain Wolf Recovery plan was proposed to reintroduce grey wolves into the northern Rockies, including Yellowstone National Park. Local opposition was strong and vocal. Nearby residents worried that wolves would kill their domestic animals and perhaps cause injury to humans. Ranchers and hunters expressed concern that a top predator such as the wolf would reduce cattle, sheep, deer, and bison populations and travel outside the boundaries of the park.

Environmentalists countered that, as large predators, wolves were an essential part of the natural ecosystem that would help control the swelling populations of elk, deer, and bison and increase the numbers of eagles, pronghorn, foxes, and wolverines. An organization called the Defenders of Wildlife agreed to establish a $100,000 fund to reimburse any rancher who lost livestock because of wolves.

In May 1994, the Interior Department and the Fish and Wildlife Service finally approved the plan for reintroducing wolves into Yellowstone National Park and central Idaho. This led to the successful reintroduction of sixty-six wolves in 1995 and 1996.

Monitoring suggests that the wolves are indeed having a positive effect by controlling the populations of elk, bison, and deer. Coyote numbers have dropped, allowing smaller predators such as foxes to regain strength. The reduction of elk, deer, and bison has allowed willow and aspen trees to regenerate and restore overgrazed areas.

In addition, the grey wolves have begun to recover. They are to be taken off the endangered species list when there are ten breeding pairs in Yellowstone. Ranchers are allowed to kill wolves that attack livestock. Some have also accepted reimbursement for livestock losses from the Compensation Trust set up by the Defenders of Wildlife.