U.S, citizens must carry proof of citizenship when crossing into Mexico. Officials of the National Immigration Institute, posted at border entry points, require a passport, birth certificate, voter registration card, or any other document that proves citizenship. This is a change from the past. The law applies to all border cities, and is an attempt to implement uniform immigration laws on both northern and southern borders.

A Mexican tourist card is required for visiting Mexico beyond the border cities, or for stays longer than 72 hours. The free tourist cards are available from Mexican immigration authorities at the border and also at Mexican consulates and Mexican government tourist offices in the US. A birth certificate or other proof of US citizenship, such as voter registration, military ID showing place of birth, or passport is required to obtain the tourist card.