As a model organism, the chick has provided valuable insights into broad issues of development in higher animals. The complex interactions between genetic, hormonal environmental factors which occur in the developing chick provide a potent argument against unitary causal explanations for differences in behaviour. Study of the behaviour of the chick is also relevant to poultry science and the welfare of domesticated birds. This text reviews research on the development of brain and behaviour in the chick and juxtaposes this with similar work on other avian and, to a lesser extent, mammalian species. It provides a review of the subject and should interest workers in animal neurophysiology and behaviour, experimental psychologists, and poultry scientists.