A PASSPORT IS REQUIRED TO TRAVEL TO MEXICO.

Fill out Form DS-11: Application for a U.S. Passport online or by hand.Your local post office can also provide the necessary form with detailed instructions.Submit Form DS-11: Application For A U.S. Passport In PersonYou must submit Form DS-11 in person at an Acceptance Facility or Passport Agency.Submit Evidence of U.S. CitizenshipWhen applying for a U.S. passport in person, evidence of U.S. citizenship must be submitted with Form DS-11.Pay the Applicable FeePlease see Current Passport Fees and methods of payment.Provide One Passport PhotoTo avoid processing delays, be sure your photo meets all the requirements and are properly submitted with your application.

Processing Times:

ROUTINE SERVICEAs of ( Wednesday June 8, 2011  ), we are processing routine applications inapproximately 4-6 weeks from the time of application.
EXPEDITED SERVICEAs of ( Wednesday June 8, 2011  ), we are processing requests for expedited service in about 2-3 weeks door-to-door, when overnight delivery is requested and paid for both ways (to and from the passport agency).

Information obtained from http://travel.state.gov/passport/get/first/first_830.html. See state government website for additional details.