This late-13th-century church is best known for Benozzo Gozzoli's charming fresco cycle (1464-65) illustrating the life of St Augustine. You'll find it in the choir behind the altar. Gozzoli also painted the fresco featuring San Sebastian on the north wall, which shows the saint protecting the citizens of San Gimignano during the 1464 plague. What makes the image highly unusual is that he's helped by a bare-breasted Virgin Mary; this symbolises her maternal love for humanity.
Other notable artworks include Lippo Memmi's Madonna and Child with Archangel Michael and St John the Baptist (1317), said to be the oldest fresco in the town. On Sundays at 11am an English-language mass is celebrated in a chapel off the cloister.