Route 9 is a 135.310-mile-long (217.760 km) major east–west state highway in Massachusetts, United States. Along with U.S. Route 20, Route 2, and Interstate 90, Route 9 is one of the major east–west routes of Massachusetts. The western terminus is near the center of the city of Pittsfield. After winding through the small towns along the passes of the Berkshire Mountains, it crosses the college towns of the Pioneer Valley and then south of the Quabbin Reservoir and the rural areas of western Worcester County. Entering the city of Worcester from the southwestern corner of the city, it passes through the center of the city and forms the major commercial thoroughfare through the MetroWest suburbs of Boston, parallel to the Massachusetts Turnpike. Crossing the Route 128 freeway circling Boston, it passes through the inner suburbs of Newton and Brookline along Boylston Street, and enters Boston on Huntington Avenue, before reaching its eastern terminus at Copley Square.

U.S. Route 20 (US 20) runs its easternmost 153 miles (246 km) in the U.S. state of Massachusetts. The highway crosses the state border from New Lebanon, New York, into Hancock and runs eastward to Boston, where it ends at Route 2 in Kenmore Square. It spends the vast majority of its journey paralleling I-90, which has largely superseded US 20 for through travel. Still, US 20 directly serves many towns and local business areas which the turnpike bypasses.