In the Greater Yellowstone Area, free-ranging bison occur in Jackson Hole, Wyoming, and Yellowstone National Park. The Yellowstone population is discussed, with emphasis on changes in numbers from approximately 400 in 1968 to about 3500 now. Major influences for change initially were natural; more recently the winter road system used by snowmobiles appeared to be the dominant factor. The situation is in a state of flux. Interagency planning is in progress to address management alternatives for conflicts outside the park.