This is a study of 74 seventeenth-century music manuscripts for keyboard from Frescobaldi’s circle in Rome. Besides being an important catalogue with a precise physical description, contents, concordances and analysis, it also contains the identification of several organists on the grounds of archival research.Among the so far unpublished volumes, four original manuscripts of Girolamo Frescobaldi were discovered; these offer a new perspective of the Roman organists’ musical world, at a crossroads between oral and written practices.