Predicting the consequences of environmental change, species invasions, and restoration actions for biodiversity requires understanding the processes that assemble communities. Stochasticity – chance environmental and demographic events – is a fundamental processes of community assembly, yet we know relatively little about the role it plays in natural communities structured by resource gradients, density-dependent species interactions, or variable dispersal. Our understanding of stochasticity in community ecology remains limited because its role is typically inferred from observed patterns rather than studied directly. Tests of specific stochastic drivers and their importance for community assembly outcomes are exceptionally rare. This session features experiments that manipulate key drivers of stochasticity to understand how environmental and demographic stochasticity influences community dynamics and evolution. The talks in this session offer broad insights into how processes occurring at different scales can alter the role of stochasticity; for example, by increasing dispersal limitation, reducing community size, and altering the functional diversity of species pools. These talks will investigate the consequences of stochasticity for a diverse range of community outcomes, including extinction rates, coexistence, species and trait sorting along environmental gradients, pollination, and adaptation. By explicitly linking recent theoretical advances with experiments, this session provides general insights into how stochastic processes mediate community assembly, consequences for the stability of biological diversity and ecosystem functions, and guidance for improving successful restoration outcomes.