Abstract
Despite the National Science Foundation's recent clarification of the Broader Impacts Criterion used in grant evaluation, it is not clear that this criterion is being understood or applied consistently by grant writers or reviewers. In particular, there is still confusion about how to interpret the requirement for broadening the participation of under-represented groups in science and scepticism about the value of doing so. Much of this stems from uncertainty about why the participation of under-represented groups is desirable or beneficial in the first place. This paper distinguishes three different rationales for the importance of diversity in science and draws out the implications for the kind of diversity that is desirable, as well as how the diversity requirement of the Broader Impacts Criterion should be applied and weighed against other criteria in reviewing particular grants. I argue that there are epistemic, as well as social, benefits to diversity that can help promote scientific progress