The eleventh fascicle of the thirteenth-century manuscript Florence , Biblioteca Mediceo-Laurenziana, Pluteus 29.1 contains sixty monophonic Latin songs related to vernacular refrain forms of the period. Previous research has classified these songs as "rondelli," or Latin rondeaux, based upon their form . Their function as part of the thirteenth-century musical repertoire has received scant treatment by musicologists; thus far no definitive study of fascicle eleven has been undertaken. The purpose of this thesis is to examine the form of the pieces and to determine the probable use for which they were intended. The study first examines the manuscript itself and places it in its proper chronological and geographical position. The contents are described and the significance of the manuscript demonstrated. The style of the poetry and music of the songs in question are compared to twelfth- and thirteenth-century conductus style and are found to be closely related to that genre. The function and style of the conductus are described, and the suggestion is made that the songs in the Florence manuscript functioned in an analogous manner, so that they are best considered to be monophonic conducti. The form and style of the songs is presented in detail. The thirteenth-century theorists' definitions of the term "rondellus" are given, and it ls shown that the Florence pieces probably are not "rondelli." The study concludes with a complete edition of the songs with a critical commentary.