State Route 6 (SR 6) is part of Maine's system of numbered state highways, running from west to east across the state. Its western terminus is at the Canada–United States border near Sandy Bay (a terminus it shares with U.S. Route 201), where it connects to Quebec Route 173. Its eastern terminus is at the Canada-US border in Vanceboro, where it connects to New Brunswick Route 4. SR 6 is the only highway in Maine to terminate at the Canadian border at both ends. With a length of 207.23 miles (333.50 km), it is the third-longest state highway in Maine. Much of SR 6 runs through isolated parts of the state.