All Guests visiting Zanzibar Island must be in possession of a valid passport.
A valid passport is a passport in the traveler's name which won't expire within six months from the date of entry on Zanzibar Island. The passport should then likewise have at least 2 blank pages (consecutively).
Despite the fact that visas are available at Zanzibar International Airport, it is recommended to get your visa ahead of time. The government of Tanzania now has an online site that make the visa process very easy to get ahead of your holiday.