The terminology of initiation in ancient authors and inscriptions is not easy to understand, largely because no single text or readily discernible combination of texts elucidates it completely. It is therefore not surprising to ﬁnd signiﬁcant diversity in modern interpretations. The subject, however, has not received as comprehensive a treatment as it deserves. The present study aims at examining the terminology of initiation in mystery cults primarily in the classical and early Hellenistic periods, to see whether it is used consistently. If the terminology is consistent across the various cults, we may then be in a position to ascertain more precisely the nature and arrangement of the main rituals in the Eleusinian and Samothracian Mysteria.