Johann Albrecht Widmanstetter (1506–1557), humanist and privy councillor to popes and kings, has remained an enigmatic figure among Christian Hebraists whose views were little understood. This study leverages Widmanstetter's remarkable collection consisting of hundreds of Jewish manuscripts and printed books, most of which survive to this day. Explore in the first half the story of Jewish book production and collecting in sixteenth-century Europe through Widmanstetter's book acquisitions, librarianship, and correspondence. Delve into his unique perspective on Jewish literature and Kabbalah as the latter half of the study contextualizes the marginal notes in his library with his published works.