This article explores the role of knowledge in collective action with an examination of resistance efforts in the Jewish ghettos of Nazi-occupied Warsaw, Vilna, and Łódź during World War II. Because sustained collective resistance took place in Warsaw but not in the other two ghettos, a comparison of these cases is useful toward an understanding of the factors that facilitate collective action. Drawing on Schwartz's concept of “structured ignorance” and Snow and Benford's discussion of “empirical credibility,” I show that resistance occurred when and where Jews were able to gain information about the Nazi regime's genocidal plans and believed that information to be credible. The cases therefore suggest that in addition to being “structured,” ignorance may also be “cultured,” in the sense that there may be limits to what individuals will interpret as possible and true. Warsaw Jews fought back in part because they were able to overcome both structured and cultured ignorance, while Jews in the other ghettos were not able to overcome these barriers to collective action. Suggestions for further research are outlined.