The U.S. has agreements with over 100 countries (the " Six-Month Club ") that waive this requirement. For citizens of these countries, a passport only needs to be valid for the duration of their intended stay.
Six-Month Validity Update - U.S. Customs and Border Protection 6 Month Rule
Many countries require your passport to be valid for at least . If your passport expires sooner than this window, you may be denied boarding by your airline or entry by border officials. 6 Month Rule