How long is an Electronic System for Travel Authorization (ESTA) generally valid?

The Electronic System for Travel Authorization (ESTA) is generally valid for up to two years or until the passport associated with the ESTA expires, whichever comes first. This means that once an authorization is granted, travelers can make multiple trips to the United States within that time frame without needing to reapply for ESTA for each individual trip. This flexibility allows for better travel planning and increased convenience, as travelers do not have to undergo the ESTA application process repeatedly for trips that fall within the validity period.

In summary, the correct answer reflects the reality that ESTA is not just a one-time travel authorization but rather allows multiple entries over its validity period as long as the passport remains valid.