Few birds, if any, of the European species display as puzzling a behaviour as the Grey Cuckoo (Cuculus canorus L.). For centuries, its appearance, and migratory and reproductive patterns have been scrutinized and investigated, with varying degrees of success. Even the most sophisticated research methods have not yet provided the final account on this bird's « unconventional lifestyle » (Wyllie, 1981). The first collection of data and the first synthesis ever attempted on the Cuckoo's behaviour are preserved in the biological (...) treatises of the Aristotelian corpus which have been complemented by further details contributed by Greek and Latin authors or recorded by later compilers interested in natural science and biology. This paper aims at contributing to the history of the early stage of the Grey Cuckoo's ethology with a critical study of the ancient tradition concentrating primarily on (1) Shape and morphology; (2) Migratory and moulting processes; (3) Reproductive behaviour and the after-effects of its social parasitism for both the Cuckoo itself and the foster birds; (4) Tentative interpretation of social parasitism according to Aristotle and Theophrastus. (shrink)