A Catalogue of the Manuscripts of Christiaan Huygens inventories all known manuscripts written by Christiaan Huygens as well as all letters to or from him. Because almost all of the manuscripts are housed at the University of Leiden in a collection entitled Codices Hugeniani, the catalogue contains an inventory of that entire collection of family papers, including many involving Constantijn Huygens. In addition, because most scholars begin their research by consulting Oeuvres Complètes de Christiaan Huygens, which does not provide enough information to relocate the manuscripts edited therein, this catalogue essentially footnotes every edited piece by listing the source manuscripts page-by-page for each volume. Thus, the researcher should be able to move easily between manuscript and edition.