Scholars specializing in Greco-Roman lexicographical texts are very insistent on distinguishing between lexica, where the organizational principle is alphabetical, and glossaries, following the order of a source text from which all lemmata are culled, whether selectively or not. The third important category of lexica is that of the onomastica, organized by semantic areas and not alphabetical.

Almost all Greek lexica extant in the direct tradition date from the Byzantine period (for which see ) as a result of the fact that later lexicographers tended to supersede earlier works and caused their disappearance. However the indirect tradition, and, from the end of the nineteenth century onwards, the evidence provided by papyrological discoveries help to shed light on the history of a much older, and wide-reaching, tradition, with a high degree of methodological awareness, and a carefully thought-out range of typologies for textual presentation on the written page.