In the Renaissance, as in earlier periods, scholars often mastered new fields by working through a body of sources, making excerpts from them and filing them under topical headings in commonplace books. Johann Buxtorf (1564–1629) was the most celebrated Hebraist in the Christian learned world at a time when the study of Jewish texts of many kinds was expanding rapidly. One of his commonplace books survives, in Basel, and was the topic of this project in the framework of the Working Group "The Learned Practices of Canonical Texts." The book offers rich information about how he mastered an enormous range of material, much of which no Christian had read before, and applied it to writing an ethnography of Ashkenazic Judaism as well as to compiling bibliographical guides, lexica and a manual of letter-writing. The commonplace book also reveals the ways in which Buxtorf’s views of Judaism—and his experience as a Christian censor of Jewish books—shaped his original response to the texts he read. Taken together with other evidence, finally, it suggests some of the ways in which Buxtorf’s views of Jews and Jewish literature evolved over time.