There are over 50 places where people may cross the Mexico–United States border. There are also at least eight rail crossings and two ferry crossings along the border. Several large border cities have multiple crossings, often including one or more that bypass the center of the city and are designated for truck traffic. Several crossings have also been closed by the governments of either Mexico or the U.S., or both.
On the U.S. side, the Department of State assigns a three-letter Port of Entry code to each crossing. This code is included on the passport entry stamp or parole stamp one receives when crossing into the U.S. Note that one code may correspond to multiple crossings.