The inventories of historical printed music published by the Répertoire International des Sources Musicales (RISM) beginning in 1960 were a major achievement of post-war international cooperation between music librarians and musicologists. Although a great number of the entries in RISM's series A/I, B/I, and B/II were integrated into RISM's online catalog, in many ways the records still reflect the state of research in the 1950s and 1960s. Sixty years after the publication of its initial blue volume, RISM is in the midst of a concerted, large-scale effort to update our collective knowledge of historical printed music. This article examines the history of RISM's inventories of printed music. It also describes current efforts to bring the records up to the standards of twenty-first-century users. Just as it was over a half century ago, collaboration with experts from around the world is indispensable today. RISM calls upon libraries and archives everywhere to employ their unique collections in participating in this cooperative cataloging effort. Engaging with this initiative not only affords the opportunity to update this foundational tool of music bibliography but also enables improved cataloging toward a more nuanced understanding of printing practices and print culture.