The United States Department of State website addresses the FMM law and requirements
"All U.S. citizens entering Mexico by sea, including U.S. citizens engaged in recreational or commercial fishing in Mexican territorial waters, are required to have an FMM."
"Tourist Travel: U.S. citizens do not require a visa or a tourist card for tourist stays of 72 hours or less within the 20-30 kilometer “border zone". U.S. citizens traveling as tourists beyond the “border zone”, or entering Mexico by air, must pay a fee to obtain a tourist card, also known as an FMM, available from Mexican consulates, Mexican border crossing points, Mexican tourism offices, airports within the border zone and most airlines serving Mexico. The fee for the tourist card is generally included in the price of a plane ticket for travelers arriving by air. U.S. citizens fill out the FMM form; Mexican immigration retains the large portion and the traveler is given the small right-hand portion. This FMM is normally white, blue and green in color. It is extremely important to keep this form in a safe location. Mexican immigration agents and federal police have the authority to ask for proof of legal status in Mexico, and on occasion, U.S. citizens without documents have been detained by police. Travelers should always carry a photocopy of their passport data page and FMM. Upon exiting the country at a Mexican Immigration (INM) departure check point, U.S. citizens are required to turn in this form. We are aware of cases where U.S. citizens without their FMM have been required to change their flight (at personal expense), file a police report regarding the missing document, and visit an INM office to pay a fine and obtain a valid exit visa. In other cases, travelers have been able to continue their journey after paying a fine."
(Updated August 18, 2012)
MX Tour Assistance is dedicated to helping visitors obtain all documents required for tourist travel and commercial operation in Mexico.
Requirements and MXTA service fees differ depending on route of entry and length of stay.
How MX Tour Assist Works
Immigration forms are generally required for all vessels traveling within 24 km of Mexican territorial waters. Please see Mexican Laws section for more information.
If you are flying from within Mexico, you can purchase your immigration form in advance, so you do not have to pay at the airport or take time to fill out your form.
Click below to view requirements for persons entering mexico by land. Fees and requirements differ depending on length of stay.