The Collins–Valentine line, or Valentine–Collins line, is the boundary at approximately 45 degrees north latitude that separates the province of Quebec from the states of New York and Vermont. It was surveyed and marked by survey monuments in 1771–3 by John Collins, surveyor-general of Quebec, and Thomas Valentine, a commissioner appointed by the government of New York.

The Canada–United States border is the longest international border in the world. The boundary is 8,891 km (5,525 mi) long. The land border has two sections: Canada's border with the contiguous United States to its south, and with the U.S. state of Alaska to its west. The bi-national International Boundary Commission deals with matters relating to marking and maintaining the boundary, and the International Joint Commission deals with issues concerning boundary waters. The agencies responsible for facilitating legal passage through the international boundary are the Canada Border Services Agency (CBSA) and U.S. Customs and Border Protection (CBP).