The San Juan Ixcoi Mass is part of the San Miguel Acatan Repertory which was found in the northwestern highlands of Guatemala before being purchased by the Lilly Library at Indiana University. Even though the authorship and date of the mass cannot be established, the mass is similar to works from the Josquin generation. Not discounting the few transcription difficulties as well as isolated compositional weaknesses, the San Juan Ixcoi Mass demonstrates the reasonably high quality of music that was performed and even possibly composed in northwestern Guatemala three centuries ago. A modern performance edition of the mass complete with critical notes and commentary on the transcription is included within the thesis.