BosWash (also referred to as BoWash, BosNYwash, the Northeast Corridor, the BosWash Corridor, or simply the Northeast megalopolis) is a group of metropolitan areas in the northeastern United States, extending from Boston, Massachusetts, to Washington, D.C., including Manchester, New Hampshire; Worcester, Massachusetts; Springfield, Massachusetts; Providence, Rhode Island; Hartford, New Haven and Stamford, Connecticut; New York City; Camden, Jersey City and Newark, New Jersey; Philadelphia, Pennsylvania; Wilmington, Delaware; and Baltimore, Maryland. The geographic trend was first identified in French geographer Jean Gottmann's book Megalopolis: The Urbanized Northeastern Seaboard of the United States (1961).
Taking into account the adjacent localities as well as the main cities, the area stretching from Lewiston, Maine to Fredericksburg, Virginia is essentially a contiguously inhabited corridor that is home to more than 55 million people (based on 2006 population estimates). Were this region a separate country, it would be the 24th most-populous in the world, almost that of the United Kingdom or Italy.
According to Gottmann, BosWash "provides the whole of America with so many essential services, of the sort a community used to obtain in its 'downtown' section, that it may well deserve the nickname of Main Street of the nation." He identified two other megalopolises in the U.S. – ChiPitts and SanSan – but these terms did not achieve wide use.
In an attempt to update Gottmann's work with current trends, Virginia Tech's Metropolitan Institute outlined a "Northeast" megapolitan area extending beyond Boston and Washington, past Portland, Maine and Richmond, Virginia, and describes it as one of ten such areas in the United States.
The major cities in the BosWash megalopolis include the following (listed by state north to south, alphabetically within each state, largest cities in bold):
Several smaller metropolitan areas near the southwestern end of the corridor, including Harrisburg, Lancaster, Scranton, Wilkes-Barre, and York, Pennsylvania and Frederick and Hagerstown, Maryland are also sometimes considered part of the region, though opinions vary from geographer to geographer as to which cities are included or excluded.
| Combined Statistical Area|
| Metropolitan Statistical Area|
|33||Virginia Beach-Norfolk-Newport News||VA||1,649,457|
|44||Hartford-W. Hartford-E. Hartford||CT||1,188,841|
|62||Allentown - Bethlehem - Easton||PA-NJ||803,844|
|91||Harrisburg - Carlisle||PA||525,380|
|Combined non-CSA MSAs||11,154,833|
|Combined CSAs and MSAs||55,190,618|