When traveling with your pet, please contact your airline before booking your tickets. The procedures and rules about flying with a pet may differ according to the airline.
Normally, all dogs and cats under 8kg can travel with the passenger in the cabin and pets heavier than that travel in hold. Service dogs can always travel with the passenger in the cabin.
Please note that also your pet needs to have travel documents, and check the regulations of the country you are flying to before the journey.