Isla Mujeres has no airport. All arrivals come by ferry.
The main passenger route is from Puerto Juárez, a small terminal a few kilometres north of Cancún city centre (not the Hotel Zone). UltraMar and Magaña ferries run roughly every 30 minutes from early morning until midnight; the crossing takes about 15 minutes. This is the cheapest and most practical option for independent travellers coming from Cancún or the airport. A taxi from Cancún International Airport to Puerto Juárez takes around 25–35 minutes depending on traffic; there is also a public bus service via downtown Cancún.
A second service departs from Gran Puerto in the Cancún Hotel Zone. This is more convenient if you are staying on the strip; the crossing is slightly longer (around 30 minutes) and fares are higher, but the schedule is frequent throughout the day. The ferry docks at the main pier in the centre of town on Isla Mujeres.
Tickets are sold at the ferry terminals; there is no need to book in advance except during the busiest Mexican holiday weeks (Semana Santa, Christmas, and New Year). Take the last ferry with some margin — missing it means an unexpected overnight in Cancún or an expensive water taxi.