Under the Western Hemisphere Travel Initiative, as of January 2007, all anyone traveling by air between the United States, Canada, Mexico, Central and South America, the Caribbean, and Bermuda (including infants) is required to present a valid passport. The same applies to anyone traveling by land or sea as of January 2008.
Citizens of the United States or Canada (or of 42 other designated countries in Europe and Latin America, plus Singapore) who are visiting Mexico as tourists do not need a visa. They must, however, obtain validated tourist cards, called formas migratorias turistas, or FMTs, available at any Mexican consulate or Mexican tourist office, on flights to Mexico and at any border crossing. The tourist card is valid for 180 days and must be used within 90 days of issue. It expires when you exit the country. If you are planning to enter and leave Mexico more than once during your trip, you can ask for a multiple-entry tourist card, which is available at Mexican consulates.
To validate the tourist card, you need to present proof of citizenship to a Mexican immigration officer, either at the border or in the airport. Acceptable documentation includes a birth certificate (or certified copy), voter’s registration card, certificate of naturalization, or passport. Your driver’s license won’t suffice.
In 1999 the Mexican government instituted a tourist fee (currently around US$25), which is factored into your airfare if you fly but must be paid separately at a bank in Mexico if you cross the border by land or sea. The immigration office you visit will direct you to the nearest bank. Once you’ve paid, you’ll get a receipt, which you can bring back to the immigration office in exchange for validation of the tourist card. If you do not plan to travel south of Ensenada [1] or San Felipe [2], you are not required to pay this fee.
Tourists from countries other than the 45 countries referenced earlier must obtain visas before arriving in Mexico. Apply in person at a Mexican consulate and expect about a two-week turnaround. The Mexican Consulate General in San Diego can often issue same-day tourist visas. Required documentation includes a valid passport, valid U.S. visa for multiple entries, form I 94, proof of economic solvency (such as an international credit card), and a round-trip air ticket to Mexico. The visa fee costs about US$40.
Foreign visitors who are legal permanent residents of the United States do not need visas to visit Mexico for tourism. You can get a validated tourist card by presenting your passport and U.S. residence card at the airport or border control.
Dogs and cats may be brought into Mexico with proof of current vaccinations and a health certificate issued within 72 hours before entry into Mexico and signed by a registered veterinarian.
Links:
[1] http://www.moon.com/destinations/baja-cabo/ensenada-el-rosario/ensenada
[2] http://www.moon.com/destinations/baja-cabo/mexicali-san-felipe/san-felipe