The musical archive of the Cathedral of Puebla, Mexico, contains an extensive body of work by José Lazo Valero (1713-1778) amid music not only by local chapelmasters but also by European masters, including Guerrero and Palestrina. However, our understanding of Pueblan cathedral music from the eighteenth century on is lacking in detailed research. José Lazo Valero served as chapelmaster at the Cathedral of Puebla from 1749 to 1778. In the archive at Puebla we find his eight Responsories for Matins on the Feast Day of St. John the Baptist, various psalms, hymns, and Masses. The present work focuses on the eight Responsories for Matins of St. John the Baptist. Through an historical contextualization and musical analysis, I trace Lazo Valero’s stylistic development through the Responsories, which were written over the course of twenty years. I discuss how the Italian style that dominated music in Spain in the eighteenth century found its way into Pueblan musical practice, and how its incorporation into composition mirrored a change in liturgical thought during the same period. The Responsories show a move from the older, Spanish polychoral style to the newer, simpler gallant style of the early Classical period. Thus, Lazo Valero’s music represents an important piece of the mosaic of colonial music, for it distinguishes him as a transitional figure between the Mexican Baroque and Classical periods.