This dissertation is a descriptive study of the language varieties employed in the medieval Judeo-Italian translations of the book of Habakuk, with the object of determining and defining in synchronic and diachronic terms a unified typology for these varieties. The dissertation presents and argues in favor of the following theses:

1. The medieval varieties of Judeo-Italian are literary and classifiable as a koiné through their typology, function, and application.
2. The formation of the koiné is corollary to the geo-linguistic distribution and migration trends of native Italophone Jews.
3. The koiné, particularly in lexical and morphological detail, reflects a situation of textual polyglossia.
4. The syntax of the translations does not reflect the actual speech of native Italophone Jews, but is a stylistic function of the texts' didactic applications.
5. Judeo-Italian is one of a number of Italo-Romance literary koinai that were active in pre-16^th century Italy; its development can be viewed as parallel to and influenced by the centrifugal trends that led to the establishment of common literary Italian.

The texts are synoptically presented and provided with a critical apparatus, and collated with data from both Judeo-Italian glossaries and Latin and early Italo-Romance versions of Habakuk. The following topics are dealt with in detail:

1. Graphemic definition and phonetic manifestation; lexical type as opposed to form.
2. Phonetics and phonology; atypical asymmetric tonic vocalism in Parma 3068.
3. Inventory and analysis of all non-terminal components.
4. Identification of common phonological and morphemic elements.
5. Comparative parsings of selected sentences with alternative morpho-syntactic results, particularly in the handling of the Hebrew participle in S position, and the aspectual/ temporal relation and coordination of verbs in embedded phrases.
6. The correlation of Judeo-Italian tense to Hebrew aspect and voice.
7. Lexica of testimonies.