The Allegheny Mountain Range ( /ælɨˈɡeɪni/), also spelled Alleghany, Allegany and, informally, the Alleghenies, is part of the vast Appalachian Mountain Range of the eastern United States and Canada. It has a northeast-southwest orientation and runs for about 400 miles (640 km) from north-central Pennsylvania, through western Maryland and eastern West Virginia, to southwestern Virginia.

The Alleghenies comprise the rugged western-central portion of the Appalachians. They rise to approximately 4,862 feet (1,483 m) in northeastern West Virginia. In the east, they are dominated by a high, steep escarpment known as the Allegheny Front. In the west, they grade down into the closely associated Allegheny Plateau which extends into Ohio and Kentucky.

The name derives from the Allegheny River, which drains only a small portion of the Alleghenies in west-central Pennsylvania. The meaning of the word, which comes from the Lenape (Delaware) Indians, is not definitively known but is usually translated as "fine river". A Lenape legend tells of an ancient tribe called the "Allegewi" who lived on the river and were defeated by the Lenape.Allegheny is the early French spelling (as in Allegheny River, which was once part of New France), and Allegany is the early English spelling (as in Allegany County, Maryland, a former British Colony).