It has been known for some time that many species of birds, including domestic fowl Gallus domesticus, have an olfactory sense. However, the functional significance of avian olfaction is less clear. We review neurobiological, embryological and behavioral evidence relevant to the question of how domestic fowl use the sense of smell. Evidence suggests a potential role for olfaction in the formation of attachments to familiar objects or environments; in the elicitation of fear responses by alarm and predator-related odors; in the control of feeding and drinking; and in avoidance of noxious substances. The fact that domestic fowl can detect and respond to a wide range of odors, in a variety of behavioral contexts, has important practical implications, especially in relation to welfare and husbandry.