Neither political nor diplomatic historians can avoid working with enciphered sources. However, we mostly study their content and not their writing processes. In the wake of a new history of political information, ciphers and, more broadly, cryptographic usages, practices and cultures should be embraced by historians. By considering cryptographic sources as significant witnesses of a culture of political information, we can no longer look at them as information repositories or instances for cryptanalysis but as complex scientific and political objects. In that respect, Renaissance French ciphers form perfect study objects. They are not yet as complex and technical as in the midseventeenth or eighteenth century and show a representative variety of goals (political or diplomatic), systems (jargon, simple substitution, homophonic substitution, …) and usages. As any other early modern source, however, cryptographic sources are dispersed, incomplete and, sometimes, hardly understandable at first sight. By studying many ciphering tables, by observing encryption and decipherment practices within a correspondence, by matching the enciphered letters and the related ciphering table, by comparing cryptographic systems, we hope to rebuild, at least partly, the Renaissance French cryptographic practices.