14th Street NW/SW is a street in Northwest and Southwest quadrants of Washington, D.C., located 1.25 miles (2.01 km) west of the U.S. Capitol. It runs from the 14th Street Bridge north to Eastern Avenue.

Northbound U.S. Route 1 runs along 14th Street from the bridge to Constitution Avenue, where it turns east with US 50. US 1 southbound previously used 15th Street NW due to the ban on left turns from westbound Constitution Avenue to 14th Street, but it now uses the Ninth Street Tunnel, five blocks to the east. 14th Street crosses the National Mall and runs near the White House and through the western side of Washington's Logan Circle neighborhood.

Because it connects to one of the main bridges crossing the Potomac River into Northern Virginia, 14th Street has always been a major transportation corridor. It was the location of one of the first streetcar lines, and today it is the location of several afternoon carpooling "slug lines", which allow commuters to meet the high-occupancy vehicle requirements of I-395, the Henry G. Shirley Memorial Highway.

In the middle of the 20th century, 14th Street NW near the intersection of P Street was home to many car dealerships and was known as "auto row". The Casino Royal at 14th and H Streets was one of the city's most popular nightclubs. The street was the location of race riots in 1968 after the assassination of Martin Luther King Jr.

In the 1970s and 1980s, a portion of 14th Street became known primarily for its red-light district. Several strip clubs and massage parlors were concentrated roughly between New York Avenue and K Street, while prostitutes plied their trade around Logan Circle. However, rising land values eventually pushed out the adult businesses. The Source Theatre, founded by Bart Whiteman in 1977, was given some credit for the area's revival. Whiteman stood outside the theater to escort people inside in order to make them feel safer.

With the gentrification of the neighborhoods through which it passes – particularly downtown, Logan Circle, the U Street Corridor, and Columbia Heights – 14th Street is now known for live theater, art galleries, and trendy restaurants. Moreover, while the nominal center of the city's gay life is still Dupont Circle, the Washington Blade called 14th Street between U Street and Massachusetts Avenue (Thomas Circle) the best place to see and be seen. As of 2012, the center of gravity had shifted and Logan Circle was voted "DC's gay neighborhood."

The opening of a Whole Foods Market at 14th and P Streets in 2000 was considered a turning point for the neighborhood. The 21st century brought rapid gentrification along 14th Street, especially south of Florida Avenue. Within a decade, it had become one of the preeminent dining destinations in the Greater Washington area. In nine months of 2012 and 2013, two dozen restaurants opened on 14th Street. From 2010 to 2012, almost every block of 14th between Rhode Island and Florida Avenues had a major residential redevelopment project scheduled, adding more than 1,200 housing units and 85,000 square feet (7,900 m) of retail.

14th Street has been a major transit route ever since the Capital Traction Company streetcar line was built around the turn of the 20th century. The successor to that line is the Metrobus 14th Street Line—routes 52 & 54.

There are two Metrorail stations on 14th Street (the U Street station is one block east, at 13th and U Streets NW and is considered the most convenient stop to visit the heart of 14th St between P and V Sts NW):

• McPherson Square
    Blue Line
    Orange Line
    Silver Line
• Columbia Heights
    Green Line

The following Metrobus routes travel along the street (listed from south to north):

• 11Y (Eye St. NW to the 14th Street Bridge)
• 16C (Independence Ave to the 14th Street Bridge)
• 16E (Franklin Square to the 14th Street Bridge)
• 52 (Takoma or 14th St & Colorado Ave. to L'Enfant Plaza)
• 54 (Takoma to Metro Center)
• 59 (Takoma to Federal Triangle)
• E4 (Military Rd. to Kennedy St.)

The DC Circulator's Woodley Park–Adams Morgan–McPherson Square Metro bus line travels along 14th Street between Columbia Heights and Franklin Square.