This work, first published in 1822, was edited by Peter Paul Dobree (1782–1825) who had been entrusted with the literary remains of the eminent classical scholar Richard Porson (1759–1808). It contains the text of a ninth-century Greek lexicon compiled by Photius, Patriarch of Constantinople. The lexicon was a tool for Byzantine Greeks studying the works of ancient authors, whose language and vocabulary differed significantly from the day-to-day language spoken in the Byzantine Empire. The lexicon offers the modern scholar a wealth of information regarding ancient works that Photius had access to but are no longer extant. The edition is based on a transcription, made by Porson, of the only remaining manuscript of the lexicon: Codex Galeanus, in Trinity College Library, Cambridge. Volume 1 contains entries for the letters alpha to omicron. The edition has served as an important source for the study of Byzantine lexicography.