Allegheny Plateau, an upland forming part of the Appalachian Highlands in the eastern United States. The plateau occupies most of western Pennsylvania, part of eastern Ohio, more than half of West Virginia, and the western tip of Maryland. The upland area of southern New York is sometimes included.

The Allegheny Plateau is greatly eroded. Swift rivers and streams have cut deep valleys, leaving steep hills as remnants of the former surface. For the most part, elevations range from about 1,200 to 2,500 feet (370 to 760 m) above sea level.

The highest section is the Allegheny Mountains, also called the Alleghenies. They form the plateau's eastern edge and rise abruptly along a steep escarpment, called the Allegheny Front. In most of this area the terrain is quite rugged. Steep valleys and narrow gorges separating a series of northeast-southwest ranges are the chief characteristics. Spruce Knob, which rises to an elevation of 4,862 feet (1,482 m) in West Virginia, is the highest point.

The valleys and gentler slopes of the Alleghenies are dotted with farms on which grain is grown and dairy and beef cattle are raised. The area is rich in bituminous coal, especially in Pennsylvania, West Virginia, and Ohio. There are also deposits of petroleum and natural gas. Lumbering is an important industry, although most of the best timber has been cut. Extensive forests and numerous lakes, mountain resorts, state parks, and extensive forests provide fishing, hunting, hiking, and skiing.

The Alleghenies presented a serious barrier to the early settlement of the West. Routes across the plateau followed the valleys of several major rivers, including the Allegheny, Monongahela, Kanawha, Ohio, and Susquehanna.