Which two countries share the longest international border?

The top two countries with the longest international border are Canada and the United States, which share a border that stretches 8,891 kilometers (5,525 miles) in length.

With a total area of 9.98 million square kilometers, Canada is the second-largest country in the world and the longest international border that it shares is with the United States. The border starts at the Arctic Ocean in the north and runs south through the Rocky Mountains, the Great Plains, and the Great Lakes, before ending at the Atlantic Ocean. The Canada–United States border is also the world's longest bi-national land border.

The Canada–United States border is of great significance due to the close relationship between the two countries. It is the busiest international border in the world in terms of trade volume, with over $1 billion worth of goods and services crossing the border every day. The border is also a symbol of the close friendship and cooperation that exists between Canada and the United States.