A wallaby (/ˈwɒləbi/) is a small or middle-sized macropod native to Australia and New Guinea, with introduced populations in New Zealand, Hawaii, the United Kingdom and other countries. They belong to the same taxonomic family as kangaroos and sometimes the same genus, but kangaroos are specifically categorised into the four largest species of the family. The term "wallaby" is an informal designation generally used for any macropod that is smaller than a kangaroo or a wallaroo that has not been designated otherwise.

There are nine species (eight extant and one extinct) of the brush wallaby (genus Notamacropus). Their head and body length is 45 to 105 cm (18 to 41 in) and the tail is 33 to 75 cm (13 to 30 in) long. The 19 known species of rock-wallabies (genus Petrogale) live among rocks, usually near water; two species in this genus are endangered. The two living species of hare-wallabies (genus Lagorchestes; two other species in this genus are extinct) are small animals that have the movements and some of the habits of hares. The three species (two extant and one extinct) of nail-tail wallabies (genus Onychogalea) have one notable feature: a horny spur at the tip of the tail; its function is unknown. The seven species of pademelons or scrub wallabies (genus Thylogale) of New Guinea, the Bismarck Archipelago, and Tasmania are small and stocky, with short hind limbs and pointed noses. The swamp wallaby (genus Wallabia) is the only species in its genus. Another wallaby that is monotypic is the quokka or short-tailed scrub wallaby (genus Setonix); this species is now restricted to two offshore islands of Western Australia which are free of introduced predators. The seven species of dorcopsises or forest wallabies (genera Dorcopsis (four species, with a fifth as yet undescribed) and Dorcopsulus (two species)) are all native to the island of New Guinea.

One of the brush wallaby species, the dwarf wallaby (Notamacropus dorcopsulus), also native to New Guinea, is the smallest known wallaby species and one of the smallest known macropods. Its length is about 46 cm (18 in) from the nose to the end of the tail, and it weighs about 1.6 kg (3.5 lb).

Wallabies are hunted for meat and fur.

The name wallaby comes from Dharug walabi or waliba.^{[citation needed]} Another early name for the wallaby, in use from at least 1802, was the brush-kangaroo.

Young wallabies are referred to as "joeys", like many other marsupials. Adult male wallabies are referred to as "bucks", "boomers", or "jacks". Adult female wallabies are referred to as "does", "flyers", or "jills". A group of wallabies is called a "mob", "court", or "troupe". Scrub-dwelling and forest-dwelling wallabies are known as "pademelons" (genus Thylogale) and "dorcopsises" (genera Dorcopsis and Dorcopsulus), respectively.

Although members of most wallaby species are small, some can grow up to approximately two metres in length (from the head to the end of the tail). Their powerful hind legs are used not only for bounding at high speeds and jumping great heights, but also to administer vigorous kicks to fend off potential predators. The tammar wallaby (Notamacropus eugenii) has elastic storage in the ankle extensor tendons, without which the animal's metabolic rate might be 30–50% greater. It has also been found that the design of spring-like tendon energy savings and economical muscle force generation is key for the two distal muscle–tendon units of the tammar wallaby (Macropus-Eugenii). Wallabies also have a powerful tail that is used mostly for balance and support.

Wallabies are herbivores whose diet consists of a wide range of grasses, vegetables, leaves and other foliage. Due to recent urbanization, many wallabies now feed in rural and urban areas. Wallabies cover vast distances for food and water, which is often scarce in their environment. Mobs of wallabies often congregate around the same water hole during the dry season.