The Andes form the natural mountain border between Chile and Argentina. The range runs along much of their shared frontier, separating Chile to the west from Argentina to the east.
At about 7,000 kilometres long, the Andes are the longest continental mountain range in the world. The Chile–Argentina border is approximately 5,308 kilometres long and follows a mixture of mountain watersheds, high peaks, straight lines and lakes rather than one perfectly uniform natural feature. Many border crossings are located at high mountain passes.
The boundary was first addressed in the 1881 Boundary Treaty, while later arbitration helped settle disputed sections, particularly in Patagonia. A frequent misconception is that the border always follows the highest peaks or the exact watershed; in reality, treaties and arbitrations produced a more complicated line. The Andes also contain Aconcagua, the highest mountain outside Asia, on the Argentine side near the Chilean border.