If you have a small pet, this is not as big a deal as it is for the big ones, because your pet can stay with you. You need to call the airline on which you will be flying as early as possible to reserve a place for your pet. Your pet will need a ticket.
Airlines allow a limited number of pets on each flight, so early reservations count.
Dogs and cats that are able to fit beneath an airline seat in a carrier should be able to travel in the cabin. These carriers are truly small, measuring no more than 23 inches long x 13 inches wide x 9 inches high on American Airlines, for example, so ask for the exact dimensions and measure before you go. Cargo holds are pressurized and pets are secured in areas where the temperature most closely resembles that of the passenger cabin. Whether your pet travels in the cabin or in cargo, he will need a sturdy carrier for the trip. For cargo shipping, though, a strong, hard-sided crate is a must.