A nest box, also spelled nestbox, is a man-made enclosure provided for animals to nest in. Nest boxes are most frequently utilized for birds, in which case they are also called birdhouses or a birdbox/bird box, but some mammalian species such as bats may also use them. Placing nestboxes or roosting boxes may also be used to help maintain populations of particular species in an area. The modern nest box was invented by the British conservationist Charles Waterton in the early 19th century to encourage more birdlife and wildfowl on the nature reserve he set up on his estate.
Traditional nest boxes have existed in many civilisations, since antiquity.
Nest boxes are getting more attention because increasing industrialization, urban growth, modern construction methods, deforestation and other human activities since the mid-20th century have caused severe declines in birds' natural habitats, introducing hurdles to breeding. A nest box can help prevent bird extinction.