Most U.S. citizens who travel abroad are used to easy access to ATMs (even in very remote locations). At the moment, ATMs are not available in Cuba for U.S. travelers, though banking relationships are in the beginning stages. In theory, Cuban ATMs could work for Americans traveling abroad in the near future. For now, you’re going to need to bring cash with you and convert to the Cuban Peso at local banks. If your stopover in Mexico City is for more than a few hours, you can also pull money out in Mexican Pesos. But be warned, the Mexican Peso to Cuban Peso exchange rate is notoriously bad. You’re better off exchanging USD, EUR or CAD for Cuban Pesos. Euros and Canadian dollars historically get a more favorable exchange rate on the ground in Cuba. In theory, MasterCard is now accepted in Cuba but trying to find a merchant to accept it is difficult.