The Southern California Association of Governments (SCAG) is the metropolitan planning organization (MPO) of six of the ten counties in Southern California, serving Imperial County, Los Angeles County, Orange County, Riverside County, San Bernardino County, and Ventura County. San Diego County's MPO is the San Diego Association of Governments, which is an unrelated agency.

SCAG is the largest MPO in the United States, representing over 18.5 million people in an area covering over 38,000 square miles (98,000 km²). As the designated MPO, SCAG is mandated by the federal government to research and draw up plans for transportation, growth management, hazardous waste management, and air quality. Additional mandates exist at the state level ^[3]

SCAG's policy direction is guided by the 86-member official governing board known as the Regional Council. The Regional Council is composed of 67 Districts that include an elected representative of one or more cities of approximately equal population levels that have a geographic community of interest (except the City of Long Beach, which has two representatives). Additionally, membership in SCAG's Regional Council includes one representative from each county Board of Supervisors (except the County of Los Angeles, which has two representatives). SCAG's Regional Council also includes one representative of the Southern California Native American Tribal Governments. Finally, all members of the Los Angeles City Council are each considered members of the SCAG Regional Council, and the mayor of Los Angeles, serves as the Los Angeles City At-Large Representative.^[4]

As of December 2014, the SCAG region consists of 191 cities, six counties, and one Tribal Government. Members include:

The Southern California Association of Governments was formed on October 28, 1965, with the purpose of conducting growth forecasts and regional planning. With each new federal transportation authorization and key state legislation, SCAG’s roles and responsibilities have increased and expanded beyond transportation planning.

In recent years, SCAG has taken a leadership role in goods movement activities and its impact on the Southern California region. In 2008, the California State Legislature passed SB 375, which sets a framework and target dates to achieve Green House Gas reductions. This legislation impacts transportation planning, growth and development, housing, and land use decisions. It also expands the role of SCAG in setting regional targets.

• Hal Bernson, Los Angeles City Council member, 1979–2003, former SCAG chairman