Washington–Baltimore combined statistical area

The Washington–Baltimore combined metropolitan statistical area is a statistical area, including the overlapping metropolitan areas of Washington, D.C. and Baltimore. The region includes Central Maryland, Northern Virginia, three counties in the Eastern Panhandle of West Virginia, and one county in south-central Pennsylvania. It is the most educated, highest-income, and third-most populous combined statistical area in the United States behind New York City–Newark, NJ and Los Angeles–Long Beach.

The area is designated by the Office of Management and Budget (OMB) as the Washington–Baltimore–Arlington, DC–MD–VA–WV–PA Combined Statistical Area. It is composed primarily of two major metropolitan statistical areas (MSAs), the Washington–Arlington–Alexandria, DC–VA–MD–WV MSA and the Baltimore–Columbia–Towson, Maryland Metropolitan Statistical Area. Five smaller urban areas not contiguous to the main urban area but having strong commuting ties with the main area are included in the metropolitan area:Hagerstown–Martinsburg, Maryland–West Virginia MSA, the Chambersburg–Waynesboro, Pennsylvania MSA, the Winchester, VA–WV MSA, the California–Lexington Park, Maryland MSA, and the Easton, Maryland micropolitan statistical area (μSA).

Some counties, such as Caroline and King George County, Virginia, are not officially designated by OMB as members of this metropolitan area but still consider themselves members anyway. This is mostly due to their proximity to the area, the size of their commuter population, and by the influence of local broadcasting stations. The population of the entire Washington–Baltimore Combined Statistical Area as of the 2020 census was 9,973,383. The area's most-populous city is Washington, D.C. with a population of 689,545, and the area's most populous county is Fairfax County, Virginia, with a population of 1,150,309.

The counties and independent cities and their groupings that comprise the area are listed below with their 2012 population estimates. Central counties/cities (designated as such by OMB) for each MSA are shown in italics.

Founded in 1957, the Metropolitan Washington Council of Governments (MWCOG) is a regional organization of 23 Washington-area local governments, members of the Maryland and Virginia state legislatures, the U.S. Senate, and the U.S. House of Representatives. MWCOG provides a forum for discussion and the development of regional responses to issues regarding the environment, transportation, public safety, homeland security, affordable housing, community planning, and economic development.

The National Capital Region Transportation Planning Board, a component of MWCOG, is the federally designated Metropolitan Planning Organization for the metropolitan Washington area.

The Baltimore Metropolitan Council is the equivalent organization for the Baltimore portion of the combined Baltimore–Washington metropolitan area. The BMC, which was created in 1992 as the successor to the Regional Planning Council and Baltimore Regional Council of Governments, consists of the Baltimore region's elected executives, representing Baltimore City and Anne Arundel, Baltimore, Carroll, Harford and Howard counties.

The Baltimore Regional Transportation Board is the federally recognized Metropolitan Planning Organization for transportation planning in the Baltimore region.