A traditional argument against the idea that the Spanish Inquisition depressed scholarly activity in Spain is that it was formed in 1478, and was most active in the period 1560-1620, yet Spain experienced its Golden Age 1492-1657. We argue that the Inquisition should have had important chilling effects, especially in STEM fields, that reduced scholars’ willingness to interact with one another and diverted their efforts into other fields. To support this thesis, we provide the first systematic evidence on scholarly interaction among the universe of early modern Spanish book authors, documenting an immediate reduction in interaction after an abrupt increase in inquisitorial activity in 1559. We also document an immediate reduction in activity and output in STEM fields. Our work helps explain the puzzling disjuncture between the glory of Spanish literary and visual arts during the Golden Age, on the one hand, and the poverty of its contributions to science, on the other.