Interstate 79 (I-79) is an Interstate Highway in the Eastern United States, designated from I-77 in Charleston, West Virginia, north to Pennsylvania Route 5 (PA 5) and PA 290 in Erie, Pennsylvania. It is a primary thoroughfare through western Pennsylvania and West Virginia and makes up part of an important corridor to Buffalo, New York, and the Canada–United States border. Major metropolitan areas connected by I-79 include Charleston and Morgantown in West Virginia and Greater Pittsburgh and Erie in Pennsylvania.

In West Virginia, I-79 is known as the Jennings Randolph Expressway, named for the West Virginia representative and senator. In the three most northern counties, it is signed as part of the High Tech Corridor. For most of its Pennsylvania stretch, it is known as the Raymond P. Shafer Highway, named for the 39th Pennsylvania governor.

Except at its northern end, I-79 is located on the Allegheny Plateau. Despite the somewhat rugged terrain, the road is relatively flat. Most of the highway is at an elevation of about 1,000 to 1,200 feet (300 to 370 m) above sea level, with some lower areas near both ends and higher areas near Sutton, West Virginia. In the hillier areas, this flatness is achieved by curving around hills, along ridges, and in or partway up river valleys. From Sutton north, I-79 generally parallels the path of U.S. Route 19 (US 19).

I-79 begins at a modified full Y interchange with I-77 along the northwest bank of the Elk River just northeast of Charleston. (Instead of the expected treatment of I-77 as the primary route at this interchange, the following traffic movements are found: northbound I-77 through traffic curves to the left, while traffic to northbound I-79 exits right; southbound I-77 through traffic curves to the right and merges on the right with traffic from southbound I-79, while traffic to northbound I-79 both exits and merges on the left; southbound I-79 traffic merges on the left with traffic from southbound I-77, while traffic to northbound I-77 both exits and merges on the left.) For its first 67 miles (108 km) to a point just south of Flatwoods, I-79 is located in the watershed of the Elk River, which drains into the Kanawha River. It crosses the Elk River at Frametown and again at Sutton and never strays more than about 15 to 20 miles (24 to 32 km) from it.

I-79 enters Pennsylvania from Morgantown, West Virginia. South of Washington, it traverses mostly rural Greene County.

Between milemarkers 34 and 38, I-79 overlaps I-70 in the Washington area before heading north toward Pittsburgh.

I-79 is carried over the Ohio River by the Neville Island Bridge, approximately eight miles (13 km) northwest of Pittsburgh.

I-279 merges into I-79 in Franklin Park, just south of Wexford between mile markers 71 and 72.