If species diverge in mechanisms for defending themselves against natural enemies, enemies can specialize on individual species, which can in turn facilitate coexistence (Janzen 1970, Connell 1971). This allows for negative frequency (or density) dependence, in which rare species have an advantage, because natural enemies evolve counter-adaptations to defenses of the most common species. While this idea has existed in the literature for some time, only recently have studies begun to characterize defenses against natural enemies across many coexisting species (e.g. Becerra 2007 PNAS, Kursar et al. 2009 PNAS). In contrast, many studies characterize coexisting species for what have been termed “functional traits”, which in fact are usually traits solely related to resource acquisition (e.g. for plants: height, rooting depth). These latter studies focus on explaining coexistence through divergence in resource-use niches (cf. Hutchinson, MacArthur) but ignore the possibility of natural enemies facilitating coexistence. Exploring the role of diversity in defenses against natural enemies merits more attention, and such studies require measuring traits related to defense across coexisting species. Here, we present an ensemble of such studies. The first speaker will provide a theoretical overview of negative frequency dependence and how this can facilitate coexistence of species. He has published landmark theoretical papers on the topic. The organized oral session will then feature speakers from a variety of plant and animal systems. One talk will focus on the role of divergence in anti-herbivore defenses in facilitating coexistence of trees in the genus Inga (Fabaceae). Another contribution will continue in this theme, presenting data from the diverse tree genus Bursera (Burseraceae) and its natural enemies. There will be another talk at the level of entire tree communities (>200 species), which will focus on the volatile organic compounds that plant species emit to defend themselves against natural enemies. A study will also be presented on fungal pathogens, their host range, and how phylogenetic signal to host preference may impact negative density dependence. Regarding animal systems, one speaker will present a study of Daphnia and how they defend themselves against natural enemies. Another talk will be grounded in empirical studies of grain moths and their pathogens. Finally, there will be a contribution on the role of parasite-mediated selection across heterogeneous environments and how this can facilitate coexistence.