The aim of this chapter is to examine how diversity benefits deliberation, information exchange and other socio-epistemic practices associated with free speech. We separate five distinct dimensions of diversity, and discuss a variety of distinct mechanisms by which various forms of diversity may be thought to have epistemically valuable outcomes. We relate these results to the moral justification of free speech. Finally, we characterise a collective action problem concerning the compliance with truth-conducive norms of deliberation, and suggest what may solve this problem.