There are many elements to international travel.
Passports are the single most important thing you must have to travel between country's.
1.) All passengers MUST have a passport to leave the USA. That includes infants traveling with the parents.
2.) The passport cannot be expired. Many international destinations require a passport to be valid for 3 months or more from date of travel.
3.) Passport cards are NOT valid for airline travel.
4.) A copy is a good thing to keep with you but NOT valid for travel.
5.) You must have a passport to check in at the airport.
6.) The name on your passport MUST match the name on your ticket.
7.) Your passport cannot been torn, coming apart at the seams, washed, or damaged in anyway.
8.) Put a phone number in the passport!
9.) Keep your passport on your person at all times!
10.) The requirements for travel to another country is the travelers responsibility. An airline agent is only required to check that you have what you need (visas, expiration dates and other requirements by the country you are traveling to or transferring in.) If you do not, you will be denied boarding.
ENJOY THE JOURNEY!