The Canada–United States land boundary is the longest in the world at 6,435 kilometers (3,999 miles). It begins in the outlet of the Passamaquoddy Bay in the Atlantic Ocean and ends in the west where the Strait of Juan de Fuca meets the Pacific Ocean. The boundary is marked by over 8,000 monuments and traverses across the Great Lakes, ten American states, seven Canadian provinces and one territory. 

The initial boundary delimitation agreement, signed in 1783 by the United Kingdom and United States, is also the Peace Treaty that ended the American Revolutionary War. From then, the boundary underwent multiple changes as the United States expanded westward and was eventually finalized and demarcated in 1925. A permanent International Boundary Commission was also established, which continues to update, maintain, and settle any disputes along the expansive border. 

In addition to the land boundary between Canada and the contiguous United States, the two States share another boundary between Yukon and Alaska. Out of four potential maritime boundaries, only one has been partially delimited through the Gulf of Maine and into the Atlantic Ocean. There are several ongoing maritime boundary disputes, but the land boundary has been fully demarcated and is undisputed. 

For more on the Canada–United States land boundary check out our blog on Point Roberts as well as a general overview.