The prototypical auxiliary in Ancient Greek is eimí “to be”, which is involved in some participial periphrases conveying aspectual value and variously interacting with the synthetic forms within the inflectional paradigm. However, many other verbs are involved in the Greek periphrastic constructions, although their status as auxiliaries is still a matter of debate. Resent research in grammaticalization allows to describe the entire range of such verbs in prototypical terms, that is, as a coherent category which includes more central and peripheral, i.e. less grammaticalized members.