The Thousand Islands Bridge is an international bridge system over the Saint Lawrence River connecting northern New York in the United States with southeastern Ontario in Canada. Constructed in 1937, with additions in 1959, the bridges span the United States-Canada border in the middle of the Thousand Islands region, from which it derives its name. The bridges all carry two lanes of traffic (one in each direction) and pedestrian sidewalks, and is administered by the Thousand Islands Bridge Authority, an international agency.

The bridge is actually not a single bridge but rather a series of 5 bridges that span parts of the St. Lawrence River, ultimately connecting both banks. The southern end of the bridge connects with Interstate 81 and the northern end of the bridge connects to Highway 401 via Highway 137. There is also an interchange with the Thousand Islands Parkway on the Ontario side.

From ground-breaking ceremonies to completion, the entire Thousand Islands Bridge system took sixteen months to complete, which was ten weeks ahead of schedule. The total cost was $3,050,000. In the early years of its operation, the bridge usually had 150,000 vehicle crossings annually. Today, however, annual crossings exceed 2,000,000 vehicles.