This paper draws upon analogy with better documented slave societies (the medieval Islamic world, and the 18th-century Caribbean) to argue, first, that the institution of slavery was a major factor in fostering a discourse on the differences among foreign peoples; and secondly, that Greek ethnographic writing was informed by the experience of slavery, containing implicit justifications of slavery as an institution. It then considers the implications of these conclusions for our understanding of Greek representations of the barbarian world and for Greek contact with non-Greeks.