Route 3 is a state-numbered route in the U.S. state of Massachusetts, maintained by the Massachusetts Department of Transportation (MassDOT). Spanning approximately 56 miles (90 km) along a north–south axis, it is inventoried with U.S. Route 3 as a single route by the state. The state-numbered Route 3 travels from Bourne in the south to Cambridge in the north, while US 3 continues from Cambridge and crosses the New Hampshire state line in Tyngsborough. Mileposts on US 3 continue from those on the state-numbered Route 3.

U.S. Route 3 (US 3) is a United States Numbered Highway running 277.90 miles (447.24 km) from Cambridge, Massachusetts, through New Hampshire, to the Canada–United States border near Third Connecticut Lake, where it connects to Quebec Route 257.