Passports, Passport Cards, SENTRI, NEXUS, FAST/EXPRES, or Enhanced Drivers License Highly Recommended for Faster U.S. Entry
U.S. citizens entering the U.S. from Mexico starting June 1st, 2009 will need a U.S. passport or other accepted forms of ID to cross the border by land with less hassle.
These other forms of ID will also be accepted:
We have heard that yes, you will be granted access back into the U.S., but you may be subject to secondary inspection delays. Sometimes travelers use their birth certificate and drivers license like in the past. It is also important to consider that if you need a tourist card (aka tourist visa/FMM) from Mexican Immigration authorities, they require a passport or a passport card to issue the FMM.