Trophic interactions are rarely linear and instead form a reticulate network of multiple interactions. Mixotrophs—species that combine phototrophic and heterotrophic metabolisms—and omnivores—organisms that feed across multiple trophic levels—are prolific in both marine and terrestrial ecological communities. Because their metabolic niches span ecological guilds and trophic levels, these organisms play an important role in modulating the flux of energy and materials through and across food webs. For example, planktonic mixotrophs short-circuit nutrient remineralization processes in the surface waters of lakes and oceans, enabling additional primary production that can support larger organisms and enhance carbon export. Omnivores, in addition to increasing food web stability through generalist feeding behavior, are often relatively large, motile organisms that can couple population dynamics across metacommunities by dispersing across larger spatial scales than other community members. Despite their importance, mixotrophs and omnivores have received relatively little theoretical and empirical attention, in part because tractability often necessitates simplifying assumptions about food web structure. However, recent advances in the study of these organisms are providing new opportunities for advances. This session brings together empiricists and theoreticians studying mixotrophy and omnivory using a variety of field settings, experimental systems, and mathematical models. Presented work will highlight how these guild- and space-spanning organisms modulate community structure and ecosystem function, and how understanding their ecological roles can help us predict and manage human-altered ecosystems.