A pet is an animal that is kept for companionship and enjoyment, as opposed to livestock, laboratory animals, working animals or sport animals, which are kept for economic reasons or to perform specific jobs. The most popular pets are noted for their loyal or playful characteristics or for their attractive appearance or song. Pets can provide their owners with many health benefits. The keeping of pets has been shown to help remove stress. Walking a dog can also provide its owner (as well as the dog) with exercise, fresh air, and the opportunity for social interaction.

While in theory one could keep any animal as a pet, in practice a small number of species of mammals, especially dogs and cats, and other small animals, such as birds, have dominated the list of species kept as pets for a very long time. Fish have joined them more recently. Many of these animals are domesticated, while others, such as reptiles, are often considered exotic pets. The glofish, a genetically modified zebrafish with a bright red fluorescent color, is the first genetically modified (GM) animal to be engineered as a pet.