W ildfires are dangerous and costly. They threaten population centers and wildlife habitats, degrade watersheds, and contribute to air pollution. At the same time, they are a natural part of the ecosystem in much of the American West. The cost of fighting these fires has risen dramatically over the past decade—to an average of $1.65 billion annually. The U.S. Forest Service currently operates an aging fleet of contracted fixed-wing airtankers that provide aerial support for wildland firefighting. After two fatal crashes in 2002 led to more than half of the fleet being taken out of service, the Forest Service sought to replace its fleet with newer, safer aircraft. In support of this effort, the agency asked RAND to determine the composition of a fleet of airtankers, scoopers, and helicopters that would minimize the total social costs of wildfires, including the cost of large fires and aircraft costs.