Travel to Mexico requires valid passports, even for US Citizens. Please ensure that your passport does not expire less than 6 months from the date of entry into Mexico. Mexico has no visa requirement for US and Canada Citizens, but you will be asked to fill out a FMM form (Mexico's visitor permit) on the plane or once you land. Once you get to immigration and customs at Cancun International Airport, the agents will give you the bottom half of the FMM form to retain until you leave the country. It is VERY important that you do not lose the FMM immigration slip because you will be required to give the slip to airline staff when you leave Mexico.