Over the past three decades, the Southern California Association of Governments has evolved as the largest of nearly 700 councils of government in the United States, functioning as the Metropolitan Planning Organization for six counties: Los Angeles, Orange, San Bernardino, Riverside, Ventura and Imperial. The region encompasses a population exceeding 15 million people in an area of more than 38,000 square miles.

As the designated Metropolitan Planning Organization, SCAG is mandated by the federal government to research and develop plans for transportation, growth management, hazardous waste management and air quality.