This article draws on rich qualitative data from two national parliaments—the UK House of Commons and the German Bundestag—to examine knowledge practices in political institutions. This is an important topic, not only because parliaments play a significant role in democratic decision-making, but because it sheds light on debates about how such decision-making is based on and interacts with knowledge and evidence. By adopting an interpretive analytical approach, I analyze the ways in which those practices are shaped by the beliefs and values of parliamentary actors. Indeed, in better understanding everyday practices, beliefs, and ideational traditions, it also contributes to better explaining how components of political and parliamentary cultures contribute to knowledge use more broadly. In the House of Commons, MPs draw on a highly trusted and independent parliamentary administration; meanwhile, committees have become fruitful avenues for MPs to develop policy expertise and engage with knowledge and evidence in a non-partisan way. In the German Bundestag, MPs also develop policy expertise—in fact, they interpret their role as specialists in a “working” parliament—but their knowledge practices are more openly partisan through the structuring role of parliamentary party groups and the skepticism of “neutral” advice from research services. Consequently, committees tend to be sites of political bargaining and conflict, rather than evidence-gathering. In both cases, parliaments’ knowledge practices are shaped by wider webs of beliefs about the role of MPs within the institutions. This suggests that knowledge use in political and policy settings is shaped by broader cultural factors.