This chapter addresses the work of Jean Mabillon and Jean Hardouin. Mabillon, a Benedictine scholar, created a new field, paleography (the field that teaches how to date and authenticate handwritten texts) with the publication in 1681 of his On Diplomatics. Defending the authenticity of the documents he and his order were charged with curating, Mabillon set out criteria for determining authenticity. The handwriting in question, the location where the manuscript was produced, and dating formulas: these aspects and more came into play. The book succeeded, not least because Mabillon published exact replicas of the documents in question. Printing had evolved into a tool that could build trust in books as truth-bearing instruments. By contrast, Jean Hardouin came to create a wild conspiracy theory: that all of ancient literature save for a few authors was forged, as were the records of the Church Councils and even the work of Church Fathers like Saint Augustine. All of it was invented – in Hardouin’s view – by medieval theologians seeking to give themselves a backstory for their logic-chopping, sometimes heretical work. How could one know? Hardouin claimed that printing was the cause: now that so many books were printed and easily available, it was easier to compare them and thus easier to “prove” forgery.