Area code 202 is the North American telephone area code for Washington, D.C. . The area code was one of the original area codes established in October 1947 by AT&T in the North American Numbering Plan (NANP).
After the State of New Jersey with area code 201 , the District of Columbia was the second Numbering Plan Area (NPA). NPAs that covered an entire administrative region received a code in which the second digit was '0'.
As of 2012, no plans exist to overlay the 202 area code, as NANPA estimates the current supply of numbers is sufficient at least to the year 2019.  Washington is thus one of the largest cities where seven-digit dialing is still possible. However, calls are connected if the area code is dialed. There is no provision for long-distance calls within the area code. 
From 1947 to 1990, area code 202 was an unpublished alternate area code for the nearby suburbs in Maryland and Virginia , which were officially in area codes 301 and 703 , respectively. This was possible because the entire Washington metropolitan area is a single LATA . Every number on the Maryland and Virginia sides of the Washington metropolitan area was given a non-published alternate number in 202. This arrangement allowed local calls throughout the metropolitan area to be dialed using only seven digits. For example, a telephone number in Kensington, Maryland , that was officially 301-949-xxxx could be dialed as 202-949-xxxx. One side effect was that a prefix could only be duplicated in jurisdictions a safe distance from the metropolitan area, such as the Eastern Shore of Maryland or southwestern Virginia.
However, on October 1, 1990, due to pending number exhaustion, the ability to dial the suburbs using area code 202 ended. This did not free up enough numbers to meet demand on either side of the metropolitan area, forcing the split of area code 410 from 301 in 1991 and the split of area code 540 from 703 in 1995. The metro area's single-LATA status meant that several prefixes on both sides of the Potomac River were unavailable for use amid the region's continued growth, forcing 703 to be overlaid with 571 and 301's overlaying with 240.
Years after the introduction of mobile number portability , a large number of cell phone customers on the Virginia and Maryland sides of the metro have 202 numbers.