The rich collection of manuscripts put together by Mazarin was diverted from the cardinal's estate and deposited in the Royal Library in 1668. Apart from a few manuscripts acquired by the librarians of the Collège des Quatre-Nations in the eighteenth century, the Library's present collection of medieval and modern manuscripts are mainly documents that Abbé Leblond took from the book depots during the revolutionary period, particularly from the Louis-la-Culture depot in rue Saint Antoine, where most of the manuscripts from Paris religious institutions had been stocked. Since the nineteenth century, donations have enriched the collection, mainly with the papers of scholars (Faugère, Thiébaut de Berneaud, Tastu, Lebrun, Demangeon-Perpillou, Laurain-Portemer...) but also with medieval and modern manuscripts (donated by the heirs of Julien Le Roy White, Paul and Madeleine Faralicq; the bequest of the Marcel Chatillon Antillean library in 2003). Acquisitions and occasional gifts continue to extend this outstanding collection. Nearly 5,000 manuscripts, ranging from the letters of Pope Leon (10th century) to contemporary scientific archives, are now kept in the Mazarine Library and made available to researchers.
- The Library's manuscripts, first catalogued in the nineteenth century, were described and referenced by Auguste Molinier (Catalogue des manuscrits de la Bibliothèque Mazarine, preface by Alfred Franklin, Paris, Plon, 1885-1892, 4 volumes). Several supplements have since been added, most recently by Pierre Gasnault in 1993.
- The entire manuscript collection is now listed and described in Calames (Online Catalogue of the Archives and Manuscripts of Tertiary Institutions). The descriptions are regularly updated, particularly with bibliographic information related to scientific studies on the manuscripts and the collections. 16,000 reproductions of illuminations from 1,400 medieval manuscripts, and certain digital facsimiles, are also accessible online.