Yes, you can book an international flight without a passport in your possession in 2026, provided you enter your full legal name exactly as it appears (or will appear) on your identification. Most airline booking systems, including major carriers like Delta and United, treat passport information as an optional field during the initial reservation phase. This allows travelers to lock in lower "early bird" fares while their passport is being renewed or processed by the government. The critical transition occurs 72 hours before departure; this is when "Secure Flight" data must be finalized for manifest purposes. You will need your valid passport number, expiration date, and country of issue to complete the online check-in process or to receive a boarding pass. It is important to note that if you book a ticket and your new passport arrives with a name variation (such as the inclusion of a middle name not on the ticket), you may face significant "name change" fees or be denied boarding. Thus, while you don't need the physical book to buy the ticket, you must be 100% certain of the legal details that will be on it.