Your passport must meet certain requirements to qualify for the Visa Waiver Program when applying with the ESTA form. Please check the general requirements as well as the country-specific details found here to ensure that your passport is acceptable for the Visa Waiver Program.
General Passport Requirements.
Machine readable passports
This type of passport will have an area on the identity page that has been encoded in a format readable by a machine. This encoded data contains the information found on the identity page.
Integrated data chips
Passports with integrated data chips are also known as e-Passports, digital passports or biometric passports. These passports include a data chip that stores personal information found on the identity page that can be read by a machine. The graphic below can be found on the front cover of your passport to indicate this type.
Temporary and emergency passports
Temporary and emergency passports must have an integrated digital chip (e-Passport type). German emergency and temporary passports do not meet the requirements of the Visa Waiver Program.
Valid official and diplomatic passports need only to be machine readable and are usable if the purpose of the trip is not for official business. If the purpose of the trip is for official business, the passport holder will not qualify for the Visa Waiver Program and must obtain a visa due to the nature of their travel purpose.
Nearly all recent machine readable UK passports will qualify as valid for the ESTA process.
If you have an extension in your UK passport, it does not meet the requirements for the Visa Waiver Program, and you cannot apply for the ESTA. If you need to travel to the United States, you can either get a new passport without an extension or apply for a visa.
Post-dated passports can be problematic when they become active near the time of travel to the United States or while on a visit to the United States. The ESTA application form's passport information must match the passport used when traveling to or within the United States. The Visa Waiver Program states that your allowable visiting period duration in the United States is up to 90 days or until you passport (used for the ESTA application) expires. You must leave the United States if the passport used for travel authorization expires, regardless if you have a post-dated passport that becomes active. Any time passport information changes, a new travel authorization must be obtained through the ESTA process.