This book provides a systematic analysis of the entire Turkish lexical corpus contained in the work traditionally known as Regola del parlare turcho. Kept in the Biblioteca Nazionale in Florence, the manuscript was written in 1533 by Filippo Argenti, who served for a number of years as secretary to the Florentine Ambassador in Istanbul. Made up of over 650 papers collected in two volumes, the code became known to scholars solely by virtue of a brief essay written in 1938 by Alessio Bombaci, who published only a small part of its content. What has hitherto remained unpublished - about 90% of the manuscript - is essentially an Italian-Turkish glossary comprising thousands of entries divided into two parts, which are named by the author as Vocabulario di nomi and Vocabulario de verbi. The material is here published in its entirety, ordered alphabetically according to the Turkish entries, and accompanied by a linguistic and historical-etymological comment on each entry which stands as a loanterm. This research is intended to fill an important gap in Turkish language studies, in that the only other material on the Turkish language published in Europe in the 16th century is fragmentary and scarce - it was not until the following century that a work comparable to Argenti's saw the light of day. The study thus stands as one of the most important contributions to recent Turkish language studies and an essential key to an understanding of the Turkish spoken in the first half of the 16th century.