What every visitor does need is a valid passport and a tourist card (or FMT - folleto de migracion turistica). Tourist cards are free, and if you're flying direct, you should get one on the plane, or from the airline before leaving. A good travel agent should be able to arrange one for you, too. Otherwise they're issued by Mexican consulates, in person or by post. Every major US city and most border towns have a Mexican consulate; tourist cards and vehicle import forms are also available from all AAA offices in California, Arizona, New Mexico and Texas. Finally, failing all these, you should be able to get tourist cards at airports or border crossings on arrival. However, if they've run out, you'll have to twiddle your thumbs until the next batch comes in, and if your passport is not issued by a rich Western country, you may encounter difficulty in persuading border officials to give you a card at all; it's therefore preferable to get one in advance.

Most people officially need a passport to pick up their tourist card, but for US and Canadian citizens all that's required is proof of citizenship (an original birth certificate or notarized copy, for instance, or naturalization papers), along with some form of photo ID (such as a driver's license). US and Canadian citizens can even enter Mexico without a passport if they carry such documents plus their tourist card with them, but it's not advisable, since officials checking your ID may not be aware of this right.

A tourist card is valid for a single entry only: if you intend to enter and leave Mexico more than once, you should pick up two or three. On the card, you are asked how long you intend to stay: always apply for longer than you need, since getting an extension is a frustrating and time-consuming business. You don't always get the time you've asked for in any case: in particular, at Mexico's borders with Belize and Guatemala to the south, you will probably only get thirty days (though they may give you more if you specifically ask), and entering via Chiapas state means you're likely only to get fifteen days (extensions unlikely). Especially if you are not from a rich country, you may also be asked to show sufficient funds for your stay.

A tourist card isn't strictly necessary for anyone who only intends to visit the northern border towns and stay less than three days (though you still need a passport or photo ID). In fact, the entire US frontier strip is a duty-free area into which you can come and go more or less as you please; heading further south beyond this zone, however, there are checkpoints on every road after about 30km, and you'll be sent back if you haven't brought the necessary documents and been through customs and immigration.

Don't lose the blue copy of your tourist card, which is given back to you after immigration inspection. You are legally required to carry it at all times, and if you have to show your papers, it's more important than your passport. Also, the blue copy must be handed in on leaving the country - without it, you may encounter hassle and delay.

Should you lose your tourist card, or need to have it renewed, head for the nearest immigration department office (Departmento de Migracion); there are downtown branches in the biggest cities. In the case of renewal, it's far simpler to cross the border for a day and get a new one on re-entry than to apply for an extension; if you do apply to the immigration department, it's wise to do so a couple of weeks in advance, though you may be told to come back nearer the actual expiry date. Whatever else you may be told, branches of SECTUR (the tourist office) cannot renew expired tourist cards or replace lost ones - they will only make sympathetic noises and direct you to the nearest immigration office.

Visas, obtainable only through a consulate (in person or by mail), are required by nationals of South Africa and most non-industrialized countries, as well as by anyone entering Mexico to work or to study for more than 180 days. Business visitors need a Business Authorization Card available from consulates, and usually a visa too. Anyone under 18 travelling without both parents needs their written consent