What documents will a US citizen need to travel in or out of Mexico?

Beginning January 23, 2007 all passengers flying between Mexico and the United States will be required to have a valid passport. Currently the government expects to implement the requirement that all travellers must present a passport or a PASS card on 1 January, 2008. This may be put into effect later than this date. The PASS card is still under development, but it will be similar in size to a driver's license and works for sea and land travel. In the past a driver's license or other state issued photo ID has been sufficient. See the Related Link for "US Government Travel Regulations" to the right for the current requirements.