Much of the debate surrounding the appropriateness of measures to protect or promote human diversity (usually embodied in attributes like language, religion, ethnicity or culture — with a significant degree of overlap between them) revolves around the question of the costs of such measures. These costs are, in fact, remarkably little-known, a fact which does not stop many commentators from making quite self-assured claims in this regard, generally to the effect that maintaining diversity is a costly indulgence. Perceptions of the costs of diversity maintenance may have far-reaching implications, including some that are put before us at this year's Francqui Prize Conference: if these costs are high, they further lessen the political legitimacy of a diversity which is already suspected of reducing people's willingness to finance economic solidarity. It is therefore useful to reflect on the question of costs, both in conceptual and in empirical terms. As will be shown in this paper, available evidence indicates that the costs of diversity maintenance are lower than is commonly believed. This does not amount to an argument that the protection or promotion of cultural diversity is an appropriate goal for public policy; however, it significantly reinforces the credibility of such an argument, while pointing to some of the weaknesses of the opposite claim.