Mont. Code Ann. § 10-3-1102

It is the purpose of this part to permit one or more fire protection services, emergency medical care providers, or local government subdivisions of this state to enter into mutual aid agreements, on the basis of mutual advantage, with one or more fire protection services, emergency medical care providers, or local government subdivisions of any other state or the United States in order to facilitate and coordinate efficient, cooperative efforts directed toward protection of life and property in areas transcending state boundaries that, due to geographic remoteness, population sparsity, and economic or other factors, are in need of those services.