The visa requirements to enter Mexico can be found at
US citizens and residents do not need a visa to enter Mexico for tourism, business or transit purposes. For non-US PhD students in US institutions we would like to highlight that they do not need a visa either. If you have a valid and unexpired visa of the following countries: Canada, the United States, Japan, the United Kingdom of Great Britain and Northern Ireland, and any of the countries of the Schengen Area, you do not need a visa to enter Mexico for tourism, business or transit purposes. All individuals in this category are required to present their valid and unexpired visa along with their passports. Both documents must be valid during your entire stay in Mexico.
If you need an invitation letter to apply for a visa to enter Mexico we are happy to provide one.
Please request it from: César Fernández-Ramírez at email@example.com