Agostino Agazzari (c. 1580-c.1642) has long been recognized as one of the most prominent theorists of the early Baroque. The enduring fame of his 1607 treatise on the basso continuo has, however, overshadowed his equally significant contributions as a composer. And for all his renown, relatively little has been written about his professional career in Siena. This book not only provides the first comprehensive study of his life and sacred works, it also opens a window on musical culture in Siena during the late sixteenth and early seventeenth centuries. Through the use of archival materials, Reardon documents Agazzari's long association with the Cathedral and furnishes valuable information on the personnel, repertory, and performance practices there. She argues for a reassessment of the influences that shaped the composer's style and challenges the generally held view that Sienese culture stagnated after the fall of the Republic in 1555.