Despite much attention to how ideas affect policy making, where these ideas come from is a blind spot in comparative political economy. We show that an important source of policy ideas are knowledge regimes—fields of policy research organizations. We show as well that the organization of knowledge regimes is heavily influenced by the organization of their surrounding political economies such that knowledge regimes have particular national characters. Furthermore, when people perceive that the utility of their knowledge regime for the rest of the political economy breaks down, they often try to restore it by transforming their knowledge regimes, albeit in ways that are still shaped by the surrounding political and economic institutions. The effectiveness of their efforts is not guaranteed. The argument is based on an analysis of the evolution of knowledge regimes since the 1970s in the USA, France and Germany. Theoretical implications are explored for two literatures in comparative political economy: ideational analysis and the varieties of capitalism.