Do you need a passport to take a cruise to cozumel?

If you are a US citizen, and the cruise ship departs and returns to the same US port, you will not need a passport to go on the cruise - as long as the cruise ship does not stop in any countries that require a passport for US citizens.

If the ship is only cruising in Mexico, and returns to the same port from which it departed, you can board the ship with a certified copy of your birth certificate and a government issued photo id.

It is much better, however, to have a passport. If, for example, there is an emergency and you have to leave the ship and fly home from Mexico, you will need a passport.