Consideration of collectives raises important questions about human rationality. This has long been known for questions about preferences, but it holds also with respect to beliefs. For one, there are contexts (such as voting) where we might care as much, or more, about the rationality of a collective than the rationality of the individuals it comprises. Here, a given standard may yield competing assessments at the individual and the collective level, thus giving rise to important normative questions. At the same time, seemingly rational strategies of individuals may have surprising consequences, or even fail, when exercised by individuals within collectives. This paper will illustrate these considerations with examples, provide an overview of different formal frameworks for understanding and assessing the beliefs of collectives, and it will illustrate how such frameworks can combine with simulations in order to elucidate epistemic norms.