This dissertation describes the musical and religious support of the Medici family to the Medici Chapel in Florence and the historical role of the church of San Lorenzo in the liturgical development of the period. During the later Middle Ages polyphony was allowed in the Office services only at Matins and Lauds during the Tenebrae service, the last three days of Holy Week, and at Vespers anytime. This practice continued until the end of the sixteenth century when more polyphonic motets based on the Antiphon and Responsory began to be included in the various Office hours during feast days. This practice is documented by the increased number of pieces that appear in the manuscripts. Two of the transcriptions from the church of San Lorenzo included in the appendix are selected from this later repertoire.