Abstract: The McCarthy era is widely understood to be the largest episode of political persecution in US history. The education sector was a major target of this persecution; specifically, academic professors and teachers were singled out.  In this paper, we study the impact of McCarthyism on scientific research. Leveraging a detailed dataset of academic publications and biographical information, we provide evidence of a decline in the professional activities of accused scientists, resulting from both the direct impact of McCarthyism on the accused scholars, as well as an indirect impact from the reaction of their community.