This may occur due to an emergency response that exceeds local resources, such as a disaster or a multiple-alarm fire.
It may also be a formal standing agreement for cooperative emergency management on a continuing basis, such as ensuring that resources are dispatched from the nearest fire station, regardless of which side of the jurisdictional boundary the incident is on.
MABAS (Mutual Aid Box Alarm System) is a regional mutual aid system, headquartered in Illinois, with 1500 member fire departments in Illinois, Indiana, Wisconsin, Iowa, Michigan, and Missouri.
The responses required from other towns are predefined, so all a dispatcher has to do is call the appropriate resources as determined by the "run card" for such an incident.
International mutual aid is also common on border communities in places such as Maine, New Hampshire, Vermont, New York, and others.