American travelers are now required to have a valid passport to travel to and from Mexico. Tourist visas are issued upon entry; you technically are allowed up to 180 days, but agents often issue just 30 or 60 days.
If you want to stay longer, request it right when you present your passport. To extend your visa, visit the immigration office in Cancún .
No special vaccines are required for travel to the Yucatán Peninsula , but it’s a good idea to be up-to-date on the standard travel immunizations, including hepatitis A, MMR (measles-mumps-rubella), tetanus-diphtheria, and typhoid.
Cancún International Airport (CUN) is far and away the most common and convenient entry point to the region. A handful of flights go directly to Cozumel  or Chetumal , and there are plans (but nothing more) for a new airport outside Tulum ; there also is an airport near Chichén Itzá , but it is used exclusively for charter flights.
An excellent network of buses, shuttles, and ferries covers the entire region, though a rental car makes a world of difference in more remote areas.
Bring to Cancún and Cozumel what you would to any beach destination: hat, sunscreen, sunglasses, flip-flops, etc. Beach buffs know to bring two or even three swimsuits, plus snorkel gear if you’ve got it. Water shoes come in handy wherever the beach is rocky, while tennis shoes and bug repellent are musts for the Maya ruins.
Finally, it’s always smart to bring an extra pair of glasses or contacts, prescription medications, birth control, and a travel clock. If you do leave anything behind, no worries—there’s a Walmart in all the major cities.