The budgerigar (/ˈbʌdʒərɪˌɡɑːr, -əriː-/ BUJ-ər-ih-gar, -⁠ə-ree-;^[3] Melopsittacus undulatus), also known as the common parakeet, shell parakeet or budgie (/ˈbʌdʒi/ BUJ-ee),^[3][4] is a small, long-tailed, seed-eating parrot. Naturally, the species is green and yellow with black, scalloped markings on the nape, back, and wings.^[5] Budgies are bred in captivity with colouring of blues, whites, yellows, greys, and even with small crests.^[5][6] Juveniles and chicks are monomorphic, while adults are told apart by their cere colouring, and their behaviour.

The species is the only member of the genus Melopsittacus, which is the only genus in the Melopsittacini tribe.

The origin of the budgerigar's name is unclear. First recorded in 1805, budgerigars are popular pets around the world due to their small size, low cost, and ability to mimic human speech. They are likely the third most popular pet in the world, after the domesticated dog and cat.^[7] Budgies are nomadic flock parakeets that have been bred in captivity since the 19th century. In both captivity and the wild, budgerigars breed opportunistically and in pairs.

They are found wild throughout the drier parts of Australia, where they have survived harsh inland conditions for over five million years. Their success can be attributed to a nomadic lifestyle and their ability to breed while on the move.^[8] The budgerigar is closely related to lories and the fig parrots