Before you make plans to travel internationally you need to verify that your passport is valid. While you wonder exactly how the passport you obtained from the U.S. Department of State is not valid, know that there are several factors in play that cause the denial of seemingly valid passports. Factors such as expiration dates, incorrect information and neglecting to obtain a new passport after a name change make your passport invalid. Even if your passport isn't slated to expire for another six months, some countries won't accept a passport that close to expiration, which is why you need to check for validity prior to travelling.
Check the expiration date on your passport, which is listed on the information page of your passport. The date listed as the expiration date is non-negotiable and if you've passed that date your passport is not valid. In addition, many international countries do not accept passports that are within six months of their expiration date, which means if you're travelling internationally in January and your passport expires in June you need to renew it before your January trip.
Compare the name on your passport with the name on your driver's license. If you were recently married or divorced or legally changed your name for any reason but neglected to renew your passport to state your new name your passport is no longer valid.
Check your passport for any damage. Normal wear and tear is expected by customs agents on U.S. passports but excessive damage could cause your passport to become invalid. Excessive damage includes water damage, missing pages, rips, tears and other things that impair the state of your passport.
Any passport not obtained from the U.S. Department of State is not valid; you cannot obtain a passport from any other office or institution.