Efforts to control brucellosis in the Greater Yellowstone Area (GYA) should focus on reducing the risk of transmission from elk, which are now viewed as the primary source of the infection in new cases occurring in cattle and domestic bison, says a new report by the National Academies of Sciences, Engineering, and Medicine. Federal, state, and tribal groups should work in a coordinated and transparent manner to address brucellosis in multiple areas and jurisdictions.