You need a passport valid for at least 6 months beyond your intended stay as well as a return ticket. US Citizens and citizens of the following countries do not require a visa to visit Mexico: Andorra, Argentina, Australia, Austria, Belgium, Canada, Chile, Costa Rica, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hong Kong, Hungary, Ireland, Island, Israel, Italy, Japan, Latvia, Liechtenstein, Lithuania, Luxembourg, Malta, Monaco, Netherlands, New Zealand, Norway, Poland, Portugal, San Marino, Singapore, Slovakia, Slovenia, South Korea, Spain, Sweden, Switzerland, United Kingdom, Uruguay, Venezuela.
Visitors are permitted to stay for up to 30 days and extensions may be granted when in the country. You may, although it is unlikely, be asked to prove that you have sufficient funds for your visit (USD 50 per person per day).
You will be asked to complete the Tourist Card, this will be handed to you by the airlines or you can obtain one from the Mexican Immigration upon arrival. This is a 'two part' document. It must be returned to the immigration department upon your departure. Make sure you keep it safe or even make a copy of it. You can apply for an extension on your card for up to 180 days.
You should always check with the appropriate consular authorities and check that you satisfy the relevant visa requirements. Visit the
Ministry of Foreign Affairs' website for current details.