Catechisms and schoolbooks were essential tools for Catholics living in partibus infidelium , ‘in the lands of the unbelievers’, in the seventeenth-century Dutch Republic. While constant demand for these texts from parents, priests and schoolteachers sustained the livelihoods of many Catholic printers, their regulation and censorship became a battleground of doctrinal orthodoxy. In the 1690s, corrections to the catechism of the Archbishop of Sens led to printed polemical rebuttals and an audit of books used in Catholic schools. Using the remarkable archival evidence surviving from this controversy, this article demonstrates the importance of schoolbooks to the Catholic book trade in the Dutch Republic and how accusations of unorthodoxy and censorship can help to reconstruct lost titles and editions.