Scholarship has rarely taken into consideration the Greek grammatical treatises on barbarism and solecism. While some of them remain unpublished down to the present day, others were edited within the large 18th- and 19th-century collections of Greek grammatical and rhetorical works, although the chosen manuscript basis was inadequate, sometimes indeed wholly arbitrary. For this reason, a new edition was urgently needed. The book is opened by a general critical overview of the phenomenon of linguistic correctness in the Greek-speaking world: it is against this benchmark of Hellenismós that barbarism and solecism acquire their sense as phenomena of corruption. The present critical edition has the ambition to publish the known ancient and Byzantine texts related to these phenomena, as they appear in manuscripts preserved throughout the world: a fresh check of all printed library catalogues has revealed 88 relevant codices, all of which are here described, philologically investigated, and used for the constitutio textus. Three texts receive here their editio princeps, others rest on a wider textual basis, and each is equipped with a selective critical apparatus: hypotheses on chronology and authorship can therefore rely on much firmer elements than before.