Most banks in Cancun are open weekdays from 9 AM-5 PM, and some are open on Saturday from 10 AM – 2 PM. Since the hours vary, it's best to go earlier in the money when the lines are shorter, the service quicker and the money available. Downtown locations are along Avenida Tulum and some of the larger banks have branches in the Hotel Zone. 

To change money into Mexican Pesos you must go to the International Money Exchange counter in any bank between 10 am and 1 pm. The exchange rate will be posted at the cashier’s desk and fluctuates daily. If you need to change money after banking hours try one of the money exchange houses but be aware that their exchange rates may not be the best and varies significantly from one place to the next. The best rate of exchange can be found in the downtown district, followed by the Hotel Zone. The worst rates are at the airport. 

You can cash traveler's checks at any of the banks, exchange houses or if you have American Express checks at their office on Avenida Tulum. You will receive the same rate as you would for cash. Bring some kind of photo identification such as a passport or driver's license. Some banks and exchange houses may ask you to complete a form with the address and phone number of your hotel. This is merely a formality. 

ATMs are found at almost every bank branch and major grocery stores. Your ATM card can be used in all the Mexican ATM machines as long as it is hooked up to a banking system such as Plus or Interact. Instructions are in both Spanish and English and the machines operate exactly as they do back home. However, you may have trouble using your ATM card if your PIN number is more than four numbers. In the afternoon, machines at the smaller banks are often out of money or take their computer systems down for servicing. If you are having problems, check one of the larger banks such as Bital, Banamex or Bancomer. All money given out will be in Mexican Pesos with the exception of one ATM machine at the airport and another at Plaza Kukulcán in the Hotel Zone. These machines dispense American money. Be sure to take your card out immediately, as the machines are quick to assume your card has been forgotten and will suck it back inside where it will remain until you visit a teller and fill out a number of forms to get your card back. 

American or Canadian Dollars are accepted in many of the hotels, restaurants and businesses at their posted exchange rate.  Check here  to find out the current exchange rate.