Yes, you can fly with a baby on your lap, typically referred to as a "lap child" or "infant in lap," provided they are under two years of age. While the FAA and most international aviation authorities allow this practice for domestic flights (often for free), safety experts and the FAA itself strongly recommend purchasing a separate seat and using an FAA-approved child restraint system (car seat). If you choose the lap option, you must still include the infant in your reservation. For international travel, even lap infants usually require a ticket, which is typically 10% of the adult fare plus taxes. Note that only one lap child is allowed per adult; if you are traveling alone with two infants, one must have a purchased seat. Once a child turns two, they are legally required to have their own seat and pay a full or child-rate fare.