U.S. Route 3 (US 3) is a north–south United States highway that runs from its southern terminus in Cambridge, Massachusetts, through New Hampshire to its terminus near Third Connecticut Lake at the Canadian border, where the road continues north as Quebec Route 257.

In New Hampshire, parts of US 3 are known as the Daniel Webster Highway. From Burlington, Massachusetts to Nashua, New Hampshire, US 3 is a freeway. (The 6.7 miles (10.8 km) in New Hampshire are a free portion of the Everett Turnpike.) A second freeway portion exists in northern New Hampshire, where US 3 utilizes the Franconia Notch Parkway and a short segment of Interstate 93, before proceeding on two-lane roads north to the border with Canada. While the southern terminus has not changed, there have been different northern termini to this route.

Massachusetts Route 3 continues beyond Boston to Cape Cod, but has never been part of US 3.