Whether a minor can travel without a passport depends entirely on the destination and the mode of transport. For domestic travel within the same country (such as a flight from New York to Los Angeles or London to Edinburgh), a minor generally does not need a passport; in fact, many airlines do not require any photo ID for children under 18 on domestic routes if they are accompanied by an adult. However, for international travel, a passport is almost universally required for all minors, including infants. One major exception for U.S. citizens is a "closed-loop" cruise (starting and ending at the same U.S. port) to specific destinations like the Bahamas or Mexico, where a minor may be able to travel with just an original birth certificate. Additionally, travel within the Schengen Area for EU citizens or within the Common Travel Area (UK and Ireland) often allows for travel with just a national ID card rather than a full passport. Regardless of the rules, it is highly recommended that a minor traveling with only one parent or a guardian carries a notarized "Letter of Consent" to prevent issues regarding international child abduction laws.