The debate about the shape of a history of knowledge in early modern Europe needs correction. It is time to finally shed light on the precarious side: the uncertainty and jeopardy of certain theories and bodies of knowledge, the delicate status of their material carriers, the reactions to threats and loss, and the risk of heretical transfers. Martin Mulsow traces this precarious knowledge with the aim of rehabilitating its significance for the process of European knowledge history. In material-rich case studies spanning the period from the Renaissance to the Enlightenment, he presents the tactics that intellectuals devised to cope with these perils, their gestures of retreat, their fears, but also their encouragements and attempts to recover lost knowledge. Precarious knowledge does not deal with the grand themes.