National Harbor is a census-designated place (CDP) in Prince George's County, Maryland, United States, located along the Potomac River near the Woodrow Wilson Bridge and just south of Washington, D.C. It originated as a 300-acre (1.2 km) multi-use waterfront development. Per the 2020 census, the population was 5,509.

National Harbor has 12 million visitors annually.

The land developed for National Harbor was previously Salubria Plantation, built in 1827 by Dr. John H. Bayne. The plantation house burned down in 1981 and was offered for sale along with the surrounding land. The land was sold in 1984 and in 1994 was rezoned for mixed-use development. In the fall of 1997, the Maryland Department of the Environment and the Army Corps of Engineers approved new developer permits, granted for the PortAmerica project in 1988.

This development has caused considerable controversy due to its environmental impacts. The Sierra Club voiced strong objections in 1999 saying that construction of National Harbor would "prevent forever the completion of the Potomac Heritage Trail". The site was linked to hundreds of thousands of gallons of untreated sewage being discharged into the Potomac River in 2008. In 2006, Peterson Companies withdrew plans to build a Target department store where the remaining plantation building, the slave quarters, still stand.

The Gaylord National Resort & Convention Center at National Harbor opened on April 1, 2008 in Oxon Hill, Maryland. The site was developed by Milton Peterson's Peterson Companies with the project expected to cost well over $2 billion, and a construction time frame of 2007 to late 2014. As of April 2016 construction was continuing and the cost was set at $4 billion. In 2010, the development was designated as a census-designated place.

The Walt Disney Company had announced that it would build a new resort hotel at National Harbor, but backed out of the project in November 2011. In 2011, Bonnie Bick, a member of the Campaign to Reinvest in the Heart of Oxon Hill suggested preserving the remaining plantation building, and making it a part of a proposed historical loop of the Potomac Heritage National Scenic Trail, as a draw for the development.

A location for the National Children's Museum opened in December 2012. The museum permanently closed in early January 2015, after announcing that it would relocate back to Washington, D.C. The museum's location is now a Local Motors facility.

On November 29, 2012, ground was broken for a Tanger Outlets shopping facility a mile east of the National Harbor waterfront, which opened in November 2013. The Capital Wheel (ferris wheel) opened in the mid-year of 2014.

An MGM-branded casino, called MGM National Harbor, opened at National Harbor on December 8, 2016, following voters' approval of an expansion to the state's gambling program in the November 2012 elections. It was built on the south side of the Beltway, about a mile northeast of the National Harbor waterfront.

On January 12, 2015, Peterson Companies announced Local Motors planned to open a location in National Harbor. On June 17, 2016, Local Motors opened their facility to the public and debuted a new vehicle named Olli. The facility includes a showroom of the company's latest vehicles, interactive STEM labs for children, and retail merchandise mostly featuring the company's brand.

On October 21, 2023, Titanic: The Exhibition, a museum in National Harbor, was open to the public. It features sculptures, models, and artifacts from the RMS Titanic, which sank on April 14, 1912.

The site has a convention center, six hotels, restaurants, shops, and condominiums. National Harbor hosted Cirque du Soleil in 2008, 2010, 2012, and 2014 and also features outdoor activities such as a culinary festival and outdoor concerts by military bands, an outdoor movie screen facing the river, an annual ice sculpture exhibition, and a Peeps Day with a Peeps eating contest. The national spelling bee competition is held there. The Gaylord National Resort & Convention Center, with 2,000 rooms, is the largest hotel between New Jersey and Florida, and the largest in the Washington area. The site includes a beachfront walking path and a connection to a bike trail on the Woodrow Wilson Bridge that crosses into Alexandria, Virginia. Amusements include a children's carousel, and the Capital Wheel, a 175-foot Ferris wheel on a pier that extends into the Potomac River. There is a fast food restaurant and a gas station among the northern ramps that provide the only ways in or out of National Harbor.

In December 2016, MGM Resorts opened MGM National Harbor, a 300-room hotel as well as a 135,000-square-foot (12,500 m) casino, stores, a spa, restaurants, a 1,200-seat theater, a 35,000-square-foot (3,300 m) convention area, and a 5,000-square-foot (460 m) parking garage.

Historical population

Census	Pop.	Note	%±
2010	3,788		—
2020	5,509		45.4%
U.S. Decennial Census 2010 2020

Melwood first appeared as a census designated place in the 2010 U.S. Census formed from part of the Fort Washington CDP.

National Harbor CDP, Maryland – Racial and ethnic composition
Note: the US Census treats Hispanic/Latino as an ethnic category. This table excludes Latinos from the racial categories and assigns them to a separate category. Hispanics/Latinos may be of any race.

Race / Ethnicity (NH = Non-Hispanic)	Pop 2010	Pop 2020	% 2010	% 2020
White alone (NH)	496	813	13.09%	14.76%
Black or African American alone (NH)	2,411	2,984	63.65%	54.17%
Native American or Alaska Native alone (NH)	4	6	0.11%	0.11%
Asian alone (NH)	409	437	10.80%	7.93%
Pacific Islander alone (NH)	2	2	0.05%	0.04%
Some Other Race alone (NH)	17	59	0.45%	1.07%
Mixed Race or Multi-Racial (NH)	93	226	2.46%	4.10%
Hispanic or Latino (any race)	356	982	9.40%	17.83%
Total	3,788	5,509	100.00%	100.00%

As of the census of 2010, there were 3,788 people, 1,598 households, and 868 families residing in the census-designated place. In 2016, prior to the opening of the MGM Casino, an estimated 7,000 staff worked at National Harbor.

According to the U.S. Census Bureau, National Harbor has a total area of 1.9 square miles (4.8 km), of which 1.4 square miles (3.7 km) is land and 0.39 square miles (1.0 km), or 21.7% (consisting of the Potomac River), is water; 300 acres are in the actual development itself.

The only routes in or out of National Harbor are several ramps north of the area that link it to nearby major roadways: Interstate 95/495 (the Capital Beltway), Interstate 295 (Anacostia Freeway), and Oxon Hill Road. Commuters traveling via Indian Head Highway may access National Harbor by utilizing the Oxon Hill Road exits. In 2007, the state funded over $500 million (~$708 million in 2023) in road improvements in order to handle the 10,000 cars expected to commute daily to National Harbor.

A water taxi line run by the Potomac Riverboat Company connects the National Harbor to Alexandria, Virginia. The City of Alexandria also runs shuttles from the water taxi terminal to King Street–Old Town station. The service costs the city about $800,000 per year.