There are two categories of visitors to Mexico: free nationalities and restricted nationalities. Travellers who fall under free nationalities only need to fill in a form to enter Mexico, while those under restricted nationalities will need to acquire a visa prior to travelling in addition to the form.
Expats from the USA, Canada, Japan, the UK or any of the Schengen countries, among others, can visit Mexico without a visa. Foreign nationals who do require a visa to visit Mexico should apply at their nearest Mexican consulate before their trip.