Prevention activities are actions designed to reduce the likelihood of an ignition in the wildlands or wildland-urban interface (WUI). Excluded are flame spread and firebrand generation processes, and related mitigation approaches, such as fuels management. This section describes preventable wildfire/WUI ignitions, recent ignition patterns over time in the United States, common prevention activities and approaches, methods for measuring the economic performance of prevention activities, recent studies that measured prevention effectiveness, and current measurement challenges.