Interstate 81 (abbreviated I-81) is an interstate highway in the eastern part of the United States. Its southern terminus is at Interstate 40 near Dandridge, Tennessee; its northern terminus is on Wellesley Island (near Fishers Landing, New York) at the Canadian border, where the Thousand Islands Bridge connects it to Highway 401, the main freeway connecting Windsor-Detroit and Toronto to Montreal.

Interstate 81 largely traces the path of the Appalachian Mountains, often paralleling its older U.S. highway counterpart, U.S. Route 11. While mostly rural, it is heavily used as a trucking corridor, often as a bypass of the busier Interstate 95 to the east.

I-81 map