If you’ve ever traveled to Mexico, you’re familiar with the FMM — the Forma Migratoria Múltiple that, for most of us, is acquired on a plane. You fill in the blanks while you’re still in the air and surrender half of the FMM when you pass through Mexican customs. Don’t lose the other half! Trying to return without your half of the FMM guarantees an eternal encounter with Mexican bureaucracy. You say you’ve never met anyone who has had that experience? I rest my case.
The Expat Almanac 