A cockatoo is any of the 21 bird species belonging to the family Cacatuidae. Along with the Psittacidae family (the true parrots) and the Nestoridae family, they make up the order Psittaciformes. The name cockatoo originated from the Malay name for these birds, Kaka(k)tua (either from kaka "Parrot" + Tuwah, or "older sister" from Kakak "sister" + Tua, "old"). Placement of the cockatoos as a separate family is fairly undisputed, but it is not resolved whether or not other living lineages of parrots (such as the Lories and Lorikeets) are as distinct as they appear. The family has an Australasian distribution, ranging from the Philippines and the eastern Indonesian islands of Wallacea to New Guinea, the Solomon Islands and Australia.

Cockatoos are, on average, larger than true parrots; however, the Cockatiel, the smallest cockatoo, is a small bird, whiles some of the largest parrots, including the Hyacinth Macaw (the longest parrot) and the flightless Kakapo (the heaviest parrot), and is true parrots. Their plumage is generally less colorful than that of the other parrots, being mainly white, grey or black with some color elsewhere. Like other parrots they have strong bills and feet.

The diet of the cockatoos is composed of seeds, tubers, corms, fruit, flowers and insects. They often feed in large flocks, particularly if they feed on the ground. Cockatoos are monogamous and nest in tree hollows.

Cockatoos are popular birds in aviculture; although, for some species, the largely illegal trade in wild-caught parrots has threatened their survival. Some cockatoo species are threatened by habitat loss and particularly by the loss of suitable hollows for nesting as large, mature trees are cleared; conversely, some species have adapted well to human changes and are considered agricultural pests.