The Baltimore–Washington metropolitan area is a combined statistical area consisting of the overlapping labor market region of the cities of Washington, D.C. and Baltimore, Maryland. 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 fourth largest combined statistical area in the United States.Officially, 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 (MSA), the Washington–Arlington–Alexandria, DC–VA–MD–WV MSA and the Baltimore–Columbia–Towson, MD MSA. In addition, six other smaller urban areas not contiguous to the main urban area but having strong commuting ties with the main area are also included in the metropolitan area. These are: the Hagerstown–Martinsburg, MD–WV MSA, the Chambersburg–Waynesboro, PA MSA, the Winchester, VA–WV MSA, the California–Lexington Park, MD MSA, the Easton, MD micropolitan statistical area (µSA), and the Cambridge, MD µSA.
Some counties such as Caroline and King George County, Virginia are not officially designated by the 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 Census Bureau's 2012 Population Estimates is 9,331,587.
The most populous city is Washington, DC, with a population of 681,170. The most populous county is Fairfax County, Virginia, with a population exceeding 1.1 million.