The present work is a contribution to the history of the Sodality of Our Lady. To satisfy a natural curiosity about the "Mother and head" of all Sodalities, its history, which lay hidden in the archives, had to be drawn out and set forth. The reason why this has been done in a monograph, rather than as part of a larger work, comprehensive of the whole Sodality field or at least of the Sodalities of Rome, is the great importance of the Prima Primaria in itself. Partial Contents: Meaning of Prima Primaria; Previous Sodalities; Non-Jesuit Sodalities; First Period Formation 1564-1595; Second Period 1595-1773; Yearly Events; Rules and Practice; Annals; Third Period 1773-1912; Documents and Statistics.