The most common question asked about traveling to Mexico is:
"Can I drink the water?"
Isla Mujeres has an extensive water purification system but, no one on the island drinks the water from the tap. Bottled water is readily available at all Restaurants, Hotels and grocery stores. There is no problem brushing your teeth using tap water and don't worry if you swallow a bit in the shower. Nine times out of ten the dreaded "tourista" is caused by too much sun and overindulging during "Happy Hour" and too few glasses of water to keep youself hydrated. Use common sense and be sure to drink lots of bottled water!
 
What to Bring
Arriving in Mexico (Airport Walk-thru)
Getting to Isla Mujeres
Arriving on Isla Mujeres
Currency

From the United States Government
Tips for Travelers to Mexico

• A valid passport or your birth certificate with embossed seal and government issued photo ID (driver's license). It is a good idea to have copies of the above including your tickets.
• Mexican Tourist Card which you will be given at the airport when you check in or on the plane. Be sure to completely fill out the Tourist Card before you land in Mexico, it will save time at immigration. Put your Tourist Card in a safe place, you will required to present it when you depart Mexico.

Travel Documents for Minors:

• A valid passport or your birth certificate with embossed seal
• When a minor is traveling alone, they must have a notarized letter signed by the parents or legal guardians giving them permission to travel.
• When a minor is traveling with one adult, provide a notarized letter signed by the parent or guardian not traveling giving them permission to travel with the other parent or guardian.
• If the minor is in the custody of one parent, a notarized custody document should be provided.
• If one parent is deceased, provide the death certificate.

Your Luggage

• Most airlines allow 2 pieces of luggage per person. If you are traveling on a charter it is a good idea to check with the company. Some charters only allow 1 piece of luggage per person.
• Be sure to tag all luggage (including your carry-on) with your name, address and phone number. If you know where you will be staying, add that information as well.
• Be sure all your travel documents, tickets, money, credit cards and traveler's checks, medications, valuables and personal items are in your carry-on or purse.
• We recommend you bring a change of clothes in your carry-on. If your luggage is "delayed" at least you'll have something to wear!
• If you are bringing anything that can be ruined if it gets wet - pack it in a plastic bag. Occasionally tropical rain storms soak the luggage on its way from the plane to baggage claim. I learned this the hard way :-)

Here's are two great tips from Cancun Online:

"If you are coming to Cancun from a cooler climate, I suggest you dress in layers for travel on the airplane.  Example, put on some shorts and T-shirt or your clothing for the warmer climate with a layer of warmer clothing on top.  This way, when you arrive you can make a quick change of clothing without having to go to a bathroom or dressing room, but be sure to leave room in your carry on.  You will be much more comfortable on your ride from the airport to your hotel!"

"If you are planning to take advantage of shopping opportunities on your visit I advise that you pack an empty carry-on or two in one of your suitcases.  This way you can fill it with your treasures for travel back home.  Be sure to tag it!"

Clothing and Personal Items

• Basic summer clothes. Be sure to bring a light jacket or sweater, it can get a bit chilly at night. Isla is very casual, t-shirts and shorts are fine anywhere, but you might want to bring something dressier for evening.
• Suntan lotion, a travel size mosquito repellent (especially in summer), your toiletry items such as shampoo, shaving gear, deodorant, tooth brush and paste, etc. If you forget anything the stores on Isla stock all of these items but the selection is small.

• Follow the crowd down the escalator to the immigration area where you will present your Tourist Card (you will be given a tourist card for each person traveling to fill out on the plane) and Passport or Birth Certificate. Remember to put your Tourist Card in a safe place, you will need it to leave the country.
• After immigration go to the baggage claim area (to your left of the immigration area) and pick up your bags. There are carts for rent next to the carousels.
• Proceed to Customs  (to the right of the baggage carousels) and present your completed customs form (usually given when you check-in at the airport or on the plane). One form is needed per family.
• Press the button... 9 times out of 10 you'll get the green light which means go on through. Every once in awhile you'll get the red light and your luggage will be searched. Be sure you do not have any OPEN food packages or fruits and vegetables. A box of Ritz crackers and a jar of peanut butter are fine as long as it's UNOPENED.
• Proceed thru customs and continue down the hall to the exit doors. On each side of you there will be booths for rental cars, time shares, etc. 

Getting to Isla

• After going through Customs, continue down the hall to the exit doors, you will be in the "Arrivals" area. There are several ways to get to the ferries to Isla from the airport.
• If you are being met, they will be waiting here. Listed on the General Info page are several airport transfer companies. 
• There are ticket booths where you can purchase transportation vouchers to Puerto Juarez. Be sure you tell them you want to go directly to Puerto Juarez or you might get there by the "scenic route" through the Hotel Zone of Cancun. 
• If you are traveling by yourself try to find someone else who is going to Isla and share the cost of the taxi. The fare from the Airport to the ferries is about $40 USD and the airport vans are $10 US per person. The ride to Puerto Juarez takes approximately 30 minutes.
• The least expensive option is to take the bus from the airport to Cancun Centro and then another bus (or taxi) to Puerto Juarez. Travel time is usually 50 - 60 minutes.

The Ferries

• The are two Ferry docks to Isla Mujeres. Puerto Juárez & Gran Puerto Cancun which is 15 minutes north of downtown Cancun. Express  boats leave every half hour and the crossing takes about 15 minutes and the fare is 35 pesos. The first crossing from Cancun is at 6:30 AM, beginning at 9:00 PM the express boats leave every hour until 12 midnight. These fast boats cost $35 pesos and the crossing takes around 15 minutes. 

When you arrive at either Puerto Juarez or Gran Puerto Cancun, there are porters waiting to help you with your luggage and load it on the ferries. Please don't forget to tip!

• The Car Ferry from Punta Sam (another 10 minutes down the road from Puerto Juarez) can accommodate cars, campers and trucks as well as people.

• When you arrive on Isla there is a taxi stand next to the pier. There are also men with "tricycles" waiting to help you with your luggage and escort you to the Hotel. Most of the hotels are located in the downtown area and are within walking distance. Be sure you have all your bags, it can get a bit confusing on the Isla dock.
• Isla's only Bank, HSBC, is almost directly across from the ferry dock. There you can exchange currency and traveler's checks. Be sure you sign your checks EXACTLY how your signature appears on your passport and/or driver's license.
• ATM machines are located throughout the airport and on Isla.