Since June 2007 the United States has been issuing electronic passports, or epassports. The epassport has advanced digital security features that make it extremely difficult to counterfeit or alter. The security ensures that you, as the bearer of the passport, are indeed the person to whom it was issued.
After the 9/11 terrorist attacks, Congress legislated that all countries whose citizens do not need Visas to enter the United States must issue epassports. The move to epassports is now worldwide, driven by the realization that paper-based passports can be too easily altered and falsified.
You know you have an epassport if it has a small gold logo printed on the cover underneath "United States of America.
To learn more about how the epassport protects your privacy and safety, see JustAskGemalto.com's Tutorial on the U.S. Electronic Passport