Connecticut Avenue is a major thoroughfare in the Northwest quadrant of Washington, D.C., and suburban Montgomery County, Maryland.

[2] Connecticut Avenue was first extended north from Rock Creek around 1890 as part of an audacious plan to create a streetcar suburb in present-day Chevy Chase, Maryland, several miles distant from Washington, D.C.

The area northwest of today's Calvert Street NW was largely farmland when Francis Newlands, a sitting Congressman from Nevada, quietly acquired more than 1,700 acres in Northwest D.C. and Maryland along a five-mile stretch from today's Woodley Park neighborhood in D.C. to Jones Bridge Road in Maryland's Montgomery County.

Beginning in 1888, Newlands and his partners graded a roadway, laid streetcar track down its center, and erected a bridge over a Rock Creek tributary.

The streetcars began operating along the line's full length in 1892, connecting to their terminus at 18th and U Streets NW via the railway's iron trestle across the Rock Creek gorge.

This section is also a major commuter route; until 2020, it had reversible lanes along most of its length that operated during the morning and evening rush hours (7–9:30 a.m. and 4–6:30 p.m.).

Mid-century-era high-rise apartments line the avenue, with elegant, older detached homes on shady side streets.

After interchanging with the Capital Beltway at Exit 33, Connecticut Avenue enters Kensington, where it is the major north-south street of the central business district.

[5] In 1890, the Rock Creek Railway began operating from a terminus on Boundary Avenue two blocks east of Connecticut Avenue; after 1892, its streetcars ran across the Rock Creek gorge on an iron bridge near today's Duke Ellington Bridge, then turned north onto Connecticut near today's Calvert Street intersection.